Sincerely hope we don’t get undead NIGHT ELVES for the Horde. There’s unique elves that have been here since wrath: San’layn/vampyr elf Customization (and Allied Race idea) Coagulated Megathread {Re-VAMPed} and I’m hoping Blizzard actually listens for once if they’re going to give any sort of undead elf. Unless we get both night elves and blood elves as one, I’ll pass on yet another night elf on the Horde.
(what I said isn’t relevant to what OP did, as they said night elves on Alliance and Blood Elves on Horde, this is just a general statement.)
Otherwise, to appease the “NO MORE ELVES” crowd, undead Vry’kul would be an interesting Allied Race for an undead race. I wouldn’t play one myself, but I know there’s some people that would. I just know people have mentioned wanting undead elves for a while.