I honestly don't think it is outside the realm of possibility that Cena will, if not fully turn that night, will set into motion a heel turn. Cena vs. Miz will go on last, and I fully expect Miz to retain. Following the match, we are finally going to get the culmination of the hottest rivalry going into Mania; the Cena/Rock face off. Putting the two in front of 75,000 people that are going to be voicing their support could really decide the fate of John Cena's character.
I don't see Cena getting the support in this situation, so if I were Vince I would capitalize on it, and have Cena throw the first punch on Rock. Even go as far as Cena taking down Rock for a bit and spitting on him. Closing the show with a Rock Bottom and a People's Elbow on a "heel turned" Cena sounds like a Wrestlemania moment to me.