Been thinking about this a while... seems people on both Horde and Alliance side have been asking for a new race like the Pandaren to become playable. Problem is, it's difficult to place them, lore-wise, in one faction or the other, and it would just annoy the side that couldn't have them unless something very similar was introduced to the other (Furbolgs perhaps?).
But Blizz have shown they can get around lore issues with the DK starting chain, which frees your DK character from the control of the Lich King and you rejoin your race and faction.
So how about a hero race? Say it's the Pandaren - you start out with a phased/pseudo-instanced starting zone like the Death Knights, but you're neither Horde nor Alliance. As the quest chain progresses, you finally leave your starting zone, and you can chose your alligiance.
The disadvantage here is that you can't join a guild immediately, until you've completed the starting zone and chosen your faction.
But given that the Pandaren are reclusive and neutral, this isolation you experience at the beginning can just be woven in to the storyline.
Thoughts?
Basically if the Pandaren were introduced, they would instantly become my race of choice.