John Cena and The Rock face off against Awesome Truth. We all know there's no way this match ends controversy-free, and the most likely scenario is Cena or The Rock joining Miz and R Truth in a three-on-one beatdown. To be completely honest, it could be either one.
John Cena has been getting more boos than usual as of late, and there's no way his character liked the "We want Ryder" chants a few weeks ago in the main event of Raw when Cena and Zack Ryder teamed up against Awesome Truth. (I specify Cena's character, because John Cena the man seems to be a big fan of Ryder's.)
If Cena is ever going to have a run as a heel, the time is now, he's been listening to a growing percentage at every venue chant "CENA SUCKS" and eventually, every man reaches a point they can take no more.
While Cena is a good candidate for the heel turn, he'll always be the hero to the large percentage of the WWE's child demographic. What does this have to do with the Rock? Well, for one, those kids account for plenty of dollars spent when considering they all seem to have the newest John Cena T-shirt, likely have the newest John Cena action figure and almost certainly account for PPV buys with their vehement nagging of their parents.
This child demographic is something The Rock no longer has. When The Rock left the WWE seven years ago, most of John Cena's fans were either not born yet or still running around in their diapers. Even though CM Punk has overtaken Cena as the top seller in WWE merchandise, those kids still account for a lot of money in Vince McMahon's pockets. The WWE has been fairly adamant in the past about not wanting to turn Cena heel.
John Cena is stale and losing fans by the day, but the WWE would essentially be turning on all the little kids that love him. The Rock is going to be cheered by the fans that are 14-plus regardless of what he does—heck, he might get even more cheers from his fanbase for turning on Cena, and the WWE would be able to keep from betraying the children in the audience.