My Guess:
If the new Draenor expansion is indeed exploring more of Outlands and expanding on its lore then it makes sense that the Naga would be the new race. My theory is they will go the Panda route with Naga and have them neutral to start but eventually ending as either Alliance or Horde. The naga lore/models are already pretty developed as is so the transition to playable race would be a really simple one. Add in Visual Updates for all the current race models and that's your "hook" to go along with a possible Illidan return/Outland 2.0 expansion. =P
Either way i'm excited. Lots of good lore to work with and memorable characters and places to revisit in a new light.