That kind of thing only works in a sandbox game, and Blizz prefers to continue a single narrative than to set up a world and say 'go nuts.' And personally I prefer it this way. If you want high stakes pvp, this has never been the franchise for that.
---------- Post added 2013-04-27 at 08:00 PM ----------
While the horde/allince conflicts can't always be at the forefront, I think the game would lose something irreplaceable if you take away the factions.