Title says it all really.
You gave the Night Warrior customization options to the Night Elf Death Knights, so why not the Darkfallen customization options for Night/Blood/Void Elf Death Knights?
Heck, there’s already Darkfallen in the Ebon Blade. Just looked up ‘Lady Alistra’ - she’s been part of the order since the days they still served the Lich King and she has the crimson red eyes of a Darkfallen.
Why can’t we?