At this point they should just allow all race/class combos. Problem is Blizzard isn't willing to make druid forms and paladin mounts for all races. They still haven't given worgen or trolls their own travel forms. Just copied and pasted from night elves and tauren. But there's no good reason not to allow for all race/class combos with the exception of maybe evokers because it's dragon magic. Demon Hunters can add new races to their ranks just as Death Knights have. Gnomes and goblins can be warriors. Draenei and tauren can be rogues now. It's stupid when they justify lack of a race/class combo with "well not enough of this race is willing to do this". Especially since they're allowing tauren mages now. So few tauren don't want to be mages or warlocks because of the corruptible nature of arcane and fel magics. So with this exception there's no reason not to allow things like undead paladins or worgen and goblin monks.