I doubt they'd go to the lengths of giving every race undead options. It'd be neat, but it'd probably be more effort than they're willing to put in. Elves, probably. Orcs too.

Worgen were said to be immune to the curse of undeath in Cata, but worgen DKs are a thing, so yeah.

I imagine that if they include "light" Forsaken, they'll look like DKs but with golden eyes instead of blue. Probably a way to give people the undead paladins they've been asking for for ages.