Cena will not be turning heel!
He said everything he had to say to The Rock, and the AA on him was just to send a statement that he's not fooling around anymore with The Rock.
He said he's proud his fan's are kids, he's proud the way he dress, act's, and who he's came ot be. That's not really a saying of a guy who is a heel.
He will not turn hell for this storyline, neither would The Rock. It'll be Hogan/Rock, but both of them will be face. Who the fan's side with is basically personal opinion, but there is no need for Cena to turn heel to face Rock. He may have a more serious gimmick if he was to face him, or be maybe a tweener (that's the most he's got to being a heel).
It won't be like HBK/Hogan in 2005. Shawn turned heel so the fan's would soley be behind Hogan. The fan's are soley behind Rock already. Cena won't turn heel for one fued, becuase if he was to turn heel, he would stick with it. It would be like when Hogan and Austin turned heel, it would be that big, and they would'nt just turn him face again after one fued.
And, he's got fued's with Del Rio, Rhodes, Ziggler he's still got to go through.
So no, he does'nt have to turn heel for a fued with the Rock. Maybe more serious, or a big maybe a tweener, but that's it. He'll turn heel when his fan's get tired of him, which won't be happening for a long while. Or TNA become's competition, which won't happen ever.