To the OP of this topic -- don't worry. Cena heel turn topics are expected so much that it stopped being annoying and we just accept it as a natural part of any wrestling forum. So let me go copy and paste a response from a previous topic. -_- Anyways.
A John Cena heel turn is imminent. It has to happen eventually, whether the WWE wants it to happen or not. I don't care how many kids love your character now, there is going to come a time where that character no longer appeals to kids and merchandise sells will sink when people get sick of seeing you. More and more people are getting tired of the Cena character and its getting to the point now where just the sight of him pisses people off. So I do believe the day will come where WWE will have no choice but to turn him heel if they want him to stay relevant.
Now, do I believe that day is coming anytime soon? Not really. They missed a great opportunity to do it here in 2013 with his match against the Rock and they went with the "pasting of the torch" bit. That killed any chances of him being a bad guy anytime in 2013. Now, 2014 is up for debate and maybe even 2015. There's been a repeating cycle of HEEL TURN HYPE for John Cena each year to keep him relevant and teasing fans to stay interested. It's a sad world when the only way to keep John Cena interesting is to TEASE heel turns and it's even sadder when we all fall for it, only to be disappointed that it didn't happen. WWE should know they can't keep doing this with the fans, or Cena, for long. Something has got to give.
Cena doesn't have that many years left in him. At MAX, I see him going strong for another 5-7 years before calling it a day. Between that time, I see him going heel at least once if WWE wants to get the full 7 years usage out of him. If they don't, expect him to lose relevance in 3 years and expect the quality of the product to go down with him.