Why Grey Knights can't have Primaris

[Captain Antargo]

We have all been asking consistently and for a long time to have Grey Knights to be updated with fresh new armour and upgrades, but unless you completely erased their lore, it can't happen. here's why...

 

Grey Knights are lucky enough to have The Emperors geneseed, and that's hard to come by, and we think a  Primarchs geneseed is hard to get. The Emperor, as we all know, is dead, so no more geneseeds can be produced, so no new Primaris batches can be given them. however, their could be some ways but they would be a big risk for GW to pull off: 

 

• They could state that all the Grey Knights had been sacrificed to claim their geneseeds and then they were all given to Primaris marines
• Or, they could say that slowly over time, the Grey Knights had been slowly collecting the geneseeds from the deceased and were giving them to the Primaris.

Both of these would be extremely risky for GW to pull off as they would have a lot of angry players and wouldn't work too well with the lore either. 

 

If you have any further points or if I have missed anything, please share!

[Corvus Fortis]

No, please, not another GK primaris thread, I beg you...

 

GW won't hold new miniatures because of the lore. If they want to sell us primaris GK, they will retcon anything which gets in the way lorewise, or simply ignore the plot holes. It is not risky. How many people hated primaris? And does GW really care? Besides, GK are not nearly as popular as Vanilla marines. 

 

There is only one single reason GK doesn't have primaris - they are getting their own updated models sooner or later. 

[Skywrath]

Actually I'm going to throw your theory under the bus completely. GK will have primaris because their successor chapter the Exorcists has primaris. Unless you know of another chapter, that does the same thing, then yes, that's happening. But yeah, topics been covered to death, as Corvus pointed out.

 

Secondly, an ominous feeling I have is that won't happen for a while, imagine if they buffed us back then to be strong, so with the recent primaris stuff, we don't get left behind too far in the dust.

Edited June 17, 2020 by Skywrath

[WAR]

So here's a theory on why Grey Knights can't have Primaris:

 

Council of Nikea- Ultimately, in a speech to the gathered Astartes (which seemed to Ahzek Ahriman to be directly intended for Magnus himself^[2d]), the Emperor issued what would become known as the Edict of Nikaea, decreeing that the Legiones Astartes, beyond the use of Navigators and Astropaths, would no longer employ psykers. They were to disband their Librarius departments, the Librarians re-deployed to the battle companies and the primarchs themselves were to refrain from using any psychic powers they possessed.

 

Creation Of Grey Knights-  Grey Knights were founded on the order of the Emperor Himself, in the final bloody days of the Horus Heresy. The Emperor knew that the time was coming when He would have to face His traitorous son Horus and that He might well not survive. However, He foresaw that, even if Horus and his armies were defeated, the power of Chaos would remain a constant threat to Humanity....we know the story

 

Creation of the Primaris- For ten millennia, Archmagos Dominus Belisarius Cawl has been working on a task set for him by the Primarch Roboute Guilliman before he was mortally wounded by the Daemon Primarch Fulgrim in the days after the Horus Heresy: a new legion of transhuman warriors. Developed on orders from Guilliman 100 standard centuries past, Primaris Space Marines were diligently developed and perfected by the Priesthood of Mars during the long intervening millennia.

 

Revelation of Grey Knights- Second Founding - With great care and utmost secrecy, the Inquisitor Lords added the Grey Knights to the records of the Adeptus Terra as the 666^th Chapter of Space Marines. Lost in the anarchy of the Second Founding, so many and varied were the names and Foundings of that time that few noticed the addition of another Space Marine Chapter.

 

Indomitus Crusade- At the dawn of the Indomitus Crusade to retake the Imperium from the advancing armies of Chaos and xenos alike, Lord Commander of the Imperium Roboute Guilliman gathered his new armada, along with elements of the Adeptus Custodes, a small contingent of the Silent Sisterhood and a vast war host of Primaris Space Marines as he fought to liberate the scattered bastions of the Imperium.

 

So One Guilliman did not find out about Grey Knights until his resurrection as did Cawl. Having some psykers present from the founding stock of primaris ok, makes sense as they were hiding their abilities. But to have an army to fulfill the need and learn the Grey Knights ways nah......

[Valerian]

We have all been asking consistently and for a long time to have Grey Knights to be updated with fresh new armour and upgrades, but unless you completely erased their lore, it can't happen. here's why...

 

Grey Knights are lucky enough to have The Emperors geneseed, and that's hard to come by, and we think a  Primarchs geneseed is hard to get. The Emperor, as we all know, is dead, so no more geneseeds can be produced, so no new Primaris batches can be given them. however, their could be some ways but they would be a big risk for GW to pull off: 

 

• They could state that all the Grey Knights had been sacrificed to claim their geneseeds and then they were all given to Primaris marines
• Or, they could say that slowly over time, the Grey Knights had been slowly collecting the geneseeds from the deceased and were giving them to the Primaris.

Both of these would be extremely risky for GW to pull off as they would have a lot of angry players and wouldn't work too well with the lore either. 

 

If you have any further points or if I have missed anything, please share!

 

Every Space Marine, Grey Knight or otherwise, has two Progenoid Glands.  If I recall correctly, one can be harvested pretty much at any time after it has matured, and the other can only be harvested upon the Marine's death.  Each Progenoid Gland contains the the genetic instructions to propagate a full set of new Geneseed in a new Aspirant, so in a sense, each Marine can create two replacements.  However, the Chapter sizes are capped, and excess Geneseed goes into Chapter stockpiles, as well as the tithe to Mars, where secondary stockpiles are maintained.  These stockpiles allow the Chapters to replenish themselves relatively quickly, when they suffer greater than usual losses, and also support the creation of additional "successor" Chapters, when those are deemed necessary.

 

All that is to say that Cawl and his support staff don't need to go to the Emperor, who is not quite dead on his Golden Throne, to get new Geneseed, in exactly the same way that the Grey Knights have never needed to go back to the Emperor to get new Geneseed to make more Grey Knights.  There are 10,000 years worth of stockpiled Geneseed for Cawl to use, right there on Mars where his laboratories are.  

 

Now, Cawl presumably didn't know about the Grey Knights while he was working on the Primaris project for Guilliman (but maybe he did).  However, he has certainly learned about them, when Grand Master Voldus escorted Guilliman back to Terra.  And that was a couple hundred years ago, now.  So, he's had the last couple centuries to work on integrating 3 new Gene-seed Organs into the Gene-Seed "instructions" of the Grey Knights (derived from the Emperor himself), in the same way that he has already done successfully at least 9 other times, for the distinct Gene-seed of each of the Loyalist Primarchs.

 

I, personally, don't think that it's a huge stretch for him to be able to manage that, with enough time and resources to figure it out.  

[Valerian]

GK will have primaris because their successor chapter the Exorcists has primaris. 

 

I know some of the wikis mention the Exorcists as possible successors to the Grey Knights, unless something new has been mentioned in more recent fluff in recent years, that I'm not aware of, there is little actual evidence for this claim.  All we know is that Grey Knights are involved in the process for creating Excorcist Aspirants, because the Inquisitors in charge of that process like to keep some Grey Knights on standby, nearby, just in case something goes horribly wrong with the brief Daemonic Possession that the Exorcist is subjected to.  That aspect of the process was mentioned, if I recall correctly, in the old 3rd edition era Index Astartes for the Exorcists.  I've not seen anything that states they received their Gene-seed from the Grey Knights, and as far as my understanding of them is, their lineage is unknown.  

[Gederas]

Why Grey Knights can't have Primaris?

Answer: Because Games Workshop is waiting until they finalize the base line for Primaris before they give ANY unique Chapter units. Grey Knights would require an entirely unique set of Primaris Marines for how their force works, as well as a radically different appearance from the basic Primaris Mark X armour.

Edited June 18, 2020 by Gederas

[Skywrath]

 

 

GK will have primaris because their successor chapter the Exorcists has primaris. 

 

I know some of the wikis mention the Exorcists as possible successors to the Grey Knights, unless something new has been mentioned in more recent fluff in recent years, that I'm not aware of, there is little actual evidence for this claim.  All we know is that Grey Knights are involved in the process for creating Excorcist Aspirants, because the Inquisitors in charge of that process like to keep some Grey Knights on standby, nearby, just in case something goes horribly wrong with the brief Daemonic Possession that the Exorcist is subjected to.  That aspect of the process was mentioned, if I recall correctly, in the old 3rd edition era Index Astartes for the Exorcists.  I've not seen anything that states they received their Gene-seed from the Grey Knights, and as far as my understanding of them is, their lineage is unknown.  

 

 

Not even possible, but as confirmed. Lexicanium does this, so does 1d4chan (yes, you can scoff away if you were so inclined). Which means there might have been a development that we aren't aware of, to give them that status (I'm looking for the source as we speak). Other than that, everything about them being successors to the Grey Knights just fit - their close ties to the Inquisition, the fact that the GK are on call when they get possessed by demons, the fact they are resistant to demons is a sign their gene-seed belongs to the emperor. At this point, I think we should just ignore the official classification and just call it there - it's a well enough confirmation (at least in my eyes). 

 

EDIT: The reference is a book called Headhunted, going to see whether I can acquire a copy later tonight.

Edited June 18, 2020 by Skywrath

[Valerian]

Headhunted is the short story in an anthology about Deathwatch. This was discussed in here many years ago.

Here is an excerpt that I found:

[book Excerpt | Deathwatch: Headhunted] An Exorcist-marine is very near to granting the Emperor's Mercy to his Librarian squadmate.

Context:

Kill-team Talon is at it again, this time they've been tasked to literally retrieve an Ork Weirdboy/Boss's head, for... Inquisition business. The characters returning from the [last excerpt](https://www.reddit.com/r/40kLore/comments/9iw2vh/book_excerpt_deathwatch_exhumed_the_deathwatch/) I posted are once again: Lyandro Karras, First Codicier of the Death Spectres chapter, kill-team leader, and Darrion Rauth of the Exorcists 1st Company, Talon Two. The scene begins by Karras having decapitated the Ork, but to do so, he had to pull from the Warp more than he ever has before. There is a price to pay for tapping into the empyrean so deeply, if even for a moment.

​

Written by Steve Parker.

​

​

Karras fell to his knees, and screamed, dropping Arquemann \[a psychic force-sword\] at his side.His fight wasn't over. Not yet. Now, he turned his attention to the battle for his soul.

​

Rauth saw all too clearly that his moment had come, as he had known it must, sooner or later, but he couldn't relish it. There was no joy to be had here. Psyker or not, Lyandro Karras was a Space Marine, a son of the Emperor just as he was himself, and he had saved Rauth's life. *'But you must do it for him,'* Rauth told himself. *'You must do it to save his soul.'*

​

Out of respect, Rauth took off his helmet so that he might bear witness to the Death Spectre's final moments with his own naked eyes. Grimacing, he raised the barrel of his bolter to Karras’s temple, and began reciting the words of the *Mortis Morgatii Praetovo.* It was an ancient rite from long before the Great Crusade, forgotten by all save the Exorcists and the Grey Knights. If it worked, it would send Karras's spiritual essence beyond the reach of the warp's ravenous fiends, but it could not save his life. It was not a long rite, and Rauth recited it perfectly. As he came to the end of it he prepared to squeeze the trigger.

​

War raged inside Lyandro Karras. Sickening entities filled with hate and hunger strove to overwhelm him. They were brutal and relentless, bombarding him with unholy visions that threatened to drown him in horror and disgust.

​

He saw Imperial saints defiled and mutilated on altars of burning black rock. He saw the Golden Throne smashed and ruined, and the body of the Emperor trampled under the feet of vile capering beasts. He saw his Chapter house sundered, its walls covered in weeping sores as if the stones themselves had contracted a vile disease. He cried out, railing against the visions, denying them. But still they came.

​

He scrambled for something Cordatus \[his mentor\] had told him. Cordatus! The thought of that name alone gave him the strength to keep up the fight if only for a moment. To avoid becoming lost in empyrean, the old warrior had said, one must anchor oneself to the physical. Karras reached for the physical now, for something real, a bastion against the visions. He found it in a strange place, in a sensation he couldn't quite explain. Something hot and metallic was pressing hard against the skin of his temple. The metal was scalding him, causing him physical pain. Other pains joined it, accumulating so that the song of agony his nerves were singing became louder and louder. He felt again the pain of his burned hands, even while his gene-boosted body worked fast to heal them. He clutched at the pain, letting the sensation pull his mind back to the moment, to the here and now. He grasped it like a rock in a storm-tossed sea. The voices of the vile multitude began to weaken. He heard his own inner voice again, and immediately resumed his mantras. Soon enough, the energy of the immaterium slowed to a trickle then ceased completely. He felt the physical manifestation of his third eye closing. He felt the skin knitting on his brow once again. What was it, he wondered, this hot metal pressed to his head, this thing that had saved him?

​

He opened his eyes and saw the craggy, battle-scarred features of Darrion Rauth. The Exorcist was standing very close, helmet at his side muttering something that sounded like a prayer. His bolter was pressed to Karras's head, and he was about to blow his brains out.

​

*'What are you doing?'* Karras asked quietly. Rauth looked surprised to hear his voice.

*’I'm saving your soul, Death Spectre. Be at peace. Your honour will be spared. The daemons of the warp will not have you.’*

*’That is good to know,’* said Karras. *'Now lower your weapon. My soul is exactly where it should be, and there it stays until my service to the Emperor is done.’*

​

For a moment, neither Rauth nor Karras moved. The Exorcist did not seem convinced. *’Darrion Rauth,’* said Karras. *’Are you so eager to spill my blood? Is this why you have shadowed my every movement for the last three years?’ Perhaps Solarion \[Talon Three\] would thank you for killing me but I don't think Sigma \[inquisitor\] would.' ’That would depend,’* Rauth replied. Hesitantly, however he lowered his gun. *'You will submit to proper testing when we return to the Saint Nevarre, Sigma will insist on it, and so shall I.’*

​

*'As is your right brother, but be assured that you will find no taint. Of course it won't matter either way unless we get off this ship alive. Quickly now, grab the monster's head. I will open the cryo-case.’* Rauth did as ordered, though he kept a wary eye on the kill-team leader. Lifting Bludwrekk's lifeless head, he offered it to Karras saying, *’The machinery that boosted Bludwrekk’s power should be analysed. If other ork psykers begin to employ such things…’* Karras took the ork's head from him, placed it inside the black case, and pressed a four-digit code into the keypad on the side. The lid fused itself shut with a hiss. Karras rose, slung it over his right shoulder, sheathed Arquemann, located his helmet, and fixed it back on his head. Rauth donned his own helmet, too. *’If Sigma wanted the machine,’* said Karras as he led his comrade off the command bridge, *’he would have said so.’* Glancing at the mission chrono, he saw that barely seventeen minutes remained until the exfiltration deadline. He doubted it would be enough to escape the ship, but he wasn't about to give up without trying. Not after all they had been through here. *’Can you run?'* he asked Rauth.

Edited June 18, 2020 by Brother Lunkhead
spoilers

[Captain Coolpants]

I don't quite get the discussion. Im pretty bad with fluff in all honesty.

 

 

Why does it matter if we can't get more direct geneseed from the emperor?

 

If we can currently make replacements for our dead guys (for the past tens of thousands of years), why couldn't we do it during the primaris process? Surely it's all the same ingredients to make a replacement, just with extra primaris bits/processes?

[casb1965]

Actually I'm going to throw your theory under the bus completely. GK will have primaris because their successor chapter the Exorcists has primaris. Unless you know of another chapter, that does the same thing, then yes, that's happening. But yeah, topics been covered to death, as Corvus pointed out.

 

Secondly, an ominous feeling I have is that won't happen for a while, imagine if they buffed us back then to be strong, so with the recent primaris stuff, we don't get left behind too far in the dust.

 

But the latest SM Codex has removed any GK reference from the Exorcists and has them as an Unknown Founding Chapter, speculated to be 13th Founding and progenitor known only to the highest rankings of the Ordo Malleus.

 

 

 

 

 

[Skywrath]

 

Actually I'm going to throw your theory under the bus completely. GK will have primaris because their successor chapter the Exorcists has primaris. Unless you know of another chapter, that does the same thing, then yes, that's happening. But yeah, topics been covered to death, as Corvus pointed out.

 

Secondly, an ominous feeling I have is that won't happen for a while, imagine if they buffed us back then to be strong, so with the recent primaris stuff, we don't get left behind too far in the dust.

 

But the latest SM Codex has removed any GK reference from the Exorcists and has them as an Unknown Founding Chapter, speculated to be 13th Founding and progenitor known only to the highest rankings of the Ordo Malleus.

 

The latest codex being the 9th right? The codex that isn't released yet. Until then, I would place my trust in lexicanium or other up-to-date sources other than a codex that is over 3 years old.

 

@Captain Coolpants, and that is exactly why primaris should and will exist eventually. There is literally nothing to it. Inb4 we will get primaris when chaos primaris come out.

Edited June 18, 2020 by Skywrath

[Shagah]

 

 

Actually I'm going to throw your theory under the bus completely. GK will have primaris because their successor chapter the Exorcists has primaris. Unless you know of another chapter, that does the same thing, then yes, that's happening. But yeah, topics been covered to death, as Corvus pointed out.

 

Secondly, an ominous feeling I have is that won't happen for a while, imagine if they buffed us back then to be strong, so with the recent primaris stuff, we don't get left behind too far in the dust.

 

But the latest SM Codex has removed any GK reference from the Exorcists and has them as an Unknown Founding Chapter, speculated to be 13th Founding and progenitor known only to the highest rankings of the Ordo Malleus.

 

The latest codex being the 9th right? The codex that isn't released yet. Until then, I would place my trust in lexicanium or other up-to-date sources other than a codex that is over 3 years old.

 

@Captain Coolpants, and that is exactly why primaris should and will exist eventually. There is literally nothing to it. Inb4 we will get primaris when chaos primaris come out.

 

 

Sorry to be off topic but come on, you are calling out someone for using a 3 year old reference while relying on an 11 year old reference (the date of publication of the material referenced in the Lexicanum)?

 

The Lexicanum is a community created resource whose accuracy is only as good as the official sources that it is derived from.  As Valerian attempted to show earlier, the reference that is attributed to the origins of the Exorcists not only doe snot really demonstrate the connection, it is really old!

 

As to the actual topic, I am sure we will get Primaris in due course, and as many have already stated, any fluff around how we got it will retcon any current lore that seems to exclude it.  The actual release of any rules for GK Primaris will be entirely dependent on when GW is able to produce models which in turn will be a commercial based decision I am sure.

Edited June 19, 2020 by Shagah

[Skywrath]

 

 

 

Actually I'm going to throw your theory under the bus completely. GK will have primaris because their successor chapter the Exorcists has primaris. Unless you know of another chapter, that does the same thing, then yes, that's happening. But yeah, topics been covered to death, as Corvus pointed out.

 

Secondly, an ominous feeling I have is that won't happen for a while, imagine if they buffed us back then to be strong, so with the recent primaris stuff, we don't get left behind too far in the dust.

 

But the latest SM Codex has removed any GK reference from the Exorcists and has them as an Unknown Founding Chapter, speculated to be 13th Founding and progenitor known only to the highest rankings of the Ordo Malleus.

 

The latest codex being the 9th right? The codex that isn't released yet. Until then, I would place my trust in lexicanium or other up-to-date sources other than a codex that is over 3 years old.

 

@Captain Coolpants, and that is exactly why primaris should and will exist eventually. There is literally nothing to it. Inb4 we will get primaris when chaos primaris come out.

 

 

Sorry to be off topic but come on, you are calling out someone for using a 3 year old reference while relying on an 11 year old reference?

 

The Lexicanum is a community created resource whose accuracy is only as good as the official sources that it is derived from.  As Valerian attempted to show earlier, the reference that is attributed to the origins of the Exorcists not only doe snot really demonstrate the connection, it is really old!

 

As to the actual topic, I am sure we will get Primaris in due course, and as many have already stated, any fluff around how we got it will retcon any current lore that seems to exclude it.  The actual release of any rules for GK Primaris will be entirely dependent on when GW is able to produce models which in turn will be a commercial based decision I am sure.

 

 

How is lexicanium a 11 year old reference when some of the things there are clearly from 8th edition. Unless you mean the 8th edition is 11 years old, then I'm afraid you are simply wrong.

 

I am just saying that there is enough evidence to say Exorcists are a Grey Knight successor - their methods, the lore backs it up, their tactics. Contrary to people's belief, I don't need things to be written in stone for me to come to that conclusion, when it's clearly in front of us. And if in the off-chance it's proven to be wrong, then I'll happily eat my own words - and not a moment sooner.  

[casb1965]

 

 

Actually I'm going to throw your theory under the bus completely. GK will have primaris because their successor chapter the Exorcists has primaris. Unless you know of another chapter, that does the same thing, then yes, that's happening. But yeah, topics been covered to death, as Corvus pointed out.

 

Secondly, an ominous feeling I have is that won't happen for a while, imagine if they buffed us back then to be strong, so with the recent primaris stuff, we don't get left behind too far in the dust.

 

But the latest SM Codex has removed any GK reference from the Exorcists and has them as an Unknown Founding Chapter, speculated to be 13th Founding and progenitor known only to the highest rankings of the Ordo Malleus.

 

The latest codex being the 9th right? The codex that isn't released yet. Until then, I would place my trust in lexicanium or other up-to-date sources other than a codex that is over 3 years old.

 

@Captain Coolpants, and that is exactly why primaris should and will exist eventually. There is literally nothing to it. Inb4 we will get primaris when chaos primaris come out.

 

 

No I'm talking about the 2019 Codex, wouldn't call that b3 years old.

[Holier Than Thou]

Skywrath.

 

No offence but what I get from a lot of your posts is “I don’t care what facts/statistics/official sources/etc say, this is what I think and nothing will change that.”

 

People have pointed out that the sources you’re using to back up your arguments are not official, they are fan made articles. If you want to argue about GW’s lore, you need to use GW’s lore, not something (with all due respect to Lexicanum contributors) Joe Random has written.

Edited June 18, 2020 by Holier Than Thou

[Skywrath]

 

 

 

Actually I'm going to throw your theory under the bus completely. GK will have primaris because their successor chapter the Exorcists has primaris. Unless you know of another chapter, that does the same thing, then yes, that's happening. But yeah, topics been covered to death, as Corvus pointed out.

 

Secondly, an ominous feeling I have is that won't happen for a while, imagine if they buffed us back then to be strong, so with the recent primaris stuff, we don't get left behind too far in the dust.

 

But the latest SM Codex has removed any GK reference from the Exorcists and has them as an Unknown Founding Chapter, speculated to be 13th Founding and progenitor known only to the highest rankings of the Ordo Malleus.

 

The latest codex being the 9th right? The codex that isn't released yet. Until then, I would place my trust in lexicanium or other up-to-date sources other than a codex that is over 3 years old.

 

@Captain Coolpants, and that is exactly why primaris should and will exist eventually. There is literally nothing to it. Inb4 we will get primaris when chaos primaris come out.

 

 

No I'm talking about the 2019 Codex, wouldn't call that b3 years old.

 

 

Alright, fair enough.

 

Skywrath.

 

No offence but what I get from a lot of your posts is “I don’t care what facts/statistics/official sources/etc say, this is what I think and nothing will change that.”

 

People have pointed out that the sources you’re using to back up your arguments are not official, they are fan made articles. If you want to argue about GW’s lore, you need to use GW’s lore, not something (with all due respect to Lexicanum contributors) Joe Random has written.

 

Alright, well let me be perhaps more clear in that case. If you actually looked at the other half of my posts, then you would see that if the other's opinions make more sense, then I gladly adopt them. 

 

But what doesn't make sense to me, personally, is when there is more than one source of information backing that information up, contrary to the opinions of a few people on this forum. Sorry if that sound belittling, but even if Joe Random wrote that, there is still a grain of truth of 1% in every 99% of wrong information. Secondly, I stated numerous sources on top - are you implying that everything that doesn't have the GW logo stamped on it is wrong? Either way, this is devolving into an argument - let's just move on to the original point of this post.  

 

I apologise for causing such a ruckus though, it was definitely not my intent.

Edited June 18, 2020 by Skywrath

[Holier Than Thou]

That’s exactly what I’m stating. In a discussion about GW lore, only official GW sources carry weight. You may find something from elsewhere interesting but it’s not canon, it’s not official.

[Brother Tyler]

Whether or not the Exorcists are a Successor of the Grey Knights should be taken up in this topic (in the Index Astartes forum, where we discuss the Exorcists and other Chapters with unknown lineage). Similarly, the validity of information at external websites is a subject for the Amicus Aedes forum. This topic should remain focused on the Grey Knights and Primaris.

The in-universe explanation for why the Grey Knights don't have Primaris is probably that the existence of the Grey Knights is supposed to be a secret and that Cawl either didn't know of them or didn't have access to their gene-seed. Since Cawl has come to know about the Grey Knights after Roboute Guilliman was restored, it is possible that he has been granted access to the Grey Knights gene-seed in order to provide them with Primaris eventually. Whether or not he is ever successful in incorporating the Primaris organs into the Grey Knights gene-seed [without failure/rejection] and how long it might take to do that is unknown to us. It will be relatively easy for Games Workshop to build that lore into the Grey Knights when the time comes, and it won't represent any kind of retcon or change to the old lore.

From a real world perspective, it's probably a matter of creating the models. For the most part, the basic Primaris models work well enough with any other Chapter of the Adeptus Astartes since most of the weapons and other thematic elements are common. Small things here and there can be added by small kits (e.g., shoulder pads, etc.); and some of the bigger things (e.g., robes on the Unforgiven, muscle armour for the Blood Angels) don't appear at first and require some lore. For example, the Unforgiven didn't allow Primaris to join the Deathwing/Inner Circle - until GW sculpted an appropriate Primaris model. The Grey Knights, however, are vastly different from the other Space Marines. Their armour is distinct and they carry different weapons, each Grey Knight carries a copy of a book, etc.. So GW couldn't integrate the initial batch(es) of Primaris into the Grey Knights without a significant change to the Chapter. When GW gets around to Primaris models with appropriate Grey Knights thematic elements, the Grey Knights will get Primaris.