If I can be serious for a moment (Lance Storm FTW!), a Cena heel turn would probably make me mark out more than anything else at the moment, but he would get cheered more if he did it than he's been the last five years. Cena can never be a true heel now unless they do something drastic to get everyone to hate him. What they'd have to do is basically make him a rebel type tweener at the most because if they turn him heel, he'll just be another heel that gets cheered more than the faces. I'd love to see the kids' reactions though.