If they go with demon hunters as a new hero class they better go with mail armor. We have enough leather wearers. Mail seriously needs some love. And make sure they are VASTLY different from warlocks.
Also giving the high elves to the alliance would be a bad idea. It would give people the impression that blizzard favors the horde and are lazy. "Horde get new race ally's get a rehash.. "
(Ethrals as a neutral race would be amazing though)