Not sure how many have touched on this, however here is an idea for the dev teams working on the chaos customization.
To help fit with the philosophy that is already there, what if the current sets that are in the game i.e, Khorne bezerker for vanguard, alpha legion for sniper, and so on, got moved to being Champion sets much like the ultramarine champion pack. And then over the next content patches and the next couple of season releases the team adds in a couple of free earnable armor sets per class that have a more generic "Chaos" look to them, but still fell in with the general vibe of the class so that it would still have a more recognizable identity? 
There are quite a few "Firstborn" armor marks and variants to choose from so that Tactical and Vanguard (whose silhouettes are quite similar for the heretics) would remain easily distinguishable.
This then may open up a easier way of implementing the full range of choices for customization that the Loyalists have but now also for the Heretics. 
Of course creating these armor sets in such away so that they don't look funky with the animations already in the game will take time, I just wanted to see about helping with the idea process some!