Indeed—unfortunately, WoW is a medium where you have to get 24 guys together to go kill all the baddies with minimal thought or freedom of choice. This would be very good, but I don't know if Blizzard would want to do something so morally-gray and which would have to be so long-term, especially since players would be pretty much cheated out of the real storyline experience if they couldn't pick a side to some extent and for some characters it would be nonsensical if they were forced to pick one or the other.