During a recent WWE creative team meeting, one writer proposed the idea of a John Cena heel turn. Suffice it to say, Vince McMahon became angered and ripped him for how foolishly short-sighted the idea was.
The feeling is that with all of the merchandise revenue Cena garners, turning him heel would be a bad idea, at least until his sales cool off.
Another person close to the situation said McMahon shouldn't have lit him up because they should be open to discussing new ideas, even if they're bad. He feels discussing new ideas should be encouraged and if they're bad, simply discarded at that point.