Cosmetic skin overlays

Essentially while not adding entire new classes or abilities to the game having cosmetic skins of other imperial factions like sisters of battle, Inquisitors, assassins or custodes would be a nice visual homage without having to create entire new classes or gear. 
For example Eversor Assassin = Assault Marine, Vindicare = scout, Custodes for Heavy or Bulwark and just having unique overlays for Inquisitor or sisters with fixed physical cosmetics while being able to change color assets would add a lot of homage to other factions and fans of said factions without being overly taxing on devs.  Lastly to preserve narrative flow maybe even have them not being able to be used until you've completed one entire playthrough of the Campaign/Operations?