Just to throw a metaphorical wrench into the gear here (to potentially cause more speculation and discussion).
What if the entire build-up with Wrathion and the Legendary questline is for the Prince of the Black Dragonflight to use the power of the Celestials and his Draconic powers to unlock the "hidden potential" of the classes. Introducing a 4th spec for all classes.
It's a little cliche, but with all that's happening lately with Wrathion and his heavy-heavy-heavy involvement in the actions occurring on Pandaria, it's a possibility that any new specs could be linked to him doing something.
(The warrior Dragon Roar icon lead me down that path of speculation.. I wonder if anyone else had that thought.)