According to a source that I talked to today, there has been discussions within the WWE of making current WWE Champion John Cena a full-fledged heel in the months leading up to WrestleMania 28 and his showdown against the Rock. It should be noted that this been mentioned in the past, but has been shot down because of the tremendous merchandise he sells and the dedicated, prestigious young demo that he brings in.
One thing that is possibly holding down the turn is that Vince McMahon remains against the idea, as he has been in the past. However, McMahon has easily been swayed on ideas he has been against in the past by his close advisers that he trusts behind-the-scenes. So unless McMahon has a last minute change in direction regarding Cena’s character or one of his top advisers sell the idea to him and he ends up agreeing to it, don’t expect it to happen.