I don't see anything really huge like a Cena heel turn or The Rock actually competing to come out of this. More than likely, it'll be Rock as guest ref between Cena and Miz, the two guys he ran down when he returned.
Either of those first two scenarios would be awesome of course, but I don't think either will happen. If one of them were to happen, I'd say the Cena heel turn would be more likely....