Would that not be cool? Tactical marines could get frags attached to their belts, purity seals on their armour for tireless, and a skull on the shoulder pad for fire on the move.
Orks could get spikier bits and pieces, maybe iron gobs.
Eldar could get... I guess accentuated shoulder pads and more aspect stones on their armour, not sure how eldar customization goes.
I think it'd add some flair to the game and make units more unique.