so few of my friends were asking to play undead elf as an allied race. But Blood/Void and night elves can have dark ranger options which looks like undead.
Does that make them Undead Elves while having Dark Ranger option?
Unfortunately not. That has been a theme with shadowlands if you hadn’t noticed. Instead of adding them as separate races, anything that shares a similar body/model gets added as customizations. It’s easier.