I believe creating a completely evil playable faction could be a solution to all this black and gray morality business. Neither Alliance, nor Horde are truly evil, but they are not good either. I think that is the root of the problem. There should be at least one uncomprimisingly evil faction, but that can be neither Horde nor Alliance.
Why don't we bring back Undead Scourge, with Ner'zhul taking over Bolvar? Or something similiar to that?