I haven’t been following the leaks. The main (only?) feature is enabling character customization?

Are you seeing customized characters as more useful in the list(s) you are looking at compared to what has been available, or is it more the modeling aspects that make it interesting?

Also, why do SoB figs have to look so nice… (Me, trying hard to ignore the Celestine and sister Amalia boxes that sit in judgement on the backlog shelf)

No there is other rules for Narrative campaigns, units, detachments etc.  For me it is the Character customization, which is a throw back to the previous editions where characters had more flavor and did not have limited builds.

yes and no, They can not use the enhancements from the army only the Specialisms, Abilities, and then Weapon options (Ranged, Pistols, melee). I hated the loadout for the Warhammer Releases Jump Canoness, so with the Character Customization I am able to build my Version of her I wanted. Plus she will synergize with my Seraphim and Zephyrim a little bit. The Penitent Canoness is going to give a 4++ to Repentia so huge boost to their survivability.  Building a Custom Paragon Warsuit commander is going to be fun so the modeling aspect is there to enhance the interest. 

Jes Godwin did an amazing job creating the design. Favorite models of all the 40k line.