Though your prob wrong, it's possible that WWE would make a stupid decision like that. However, WWE hasn't always been stupid, ya know. If they take something like Cena in the future, and give him a big heel turn, that would change the way WWE is for a LONG time. Cena has always been the face of the WWE ever since he changed to a face. To take that man, and give him a baby turn, as you put it, would be a stupid move on WWE's behalf.
If your going to finally turn this baby face into a heel, you should do it right if you want to get ratings. Maybe we will see Cena team with Heyman in the future, to try and take out Punk? Who knows, I don't..maybe Cena will JOIN Punk and Heyman in the future, and try to take out HHH, or someone of the sort...they should do it right. Take Steve Austin for example, they made him heel, right? Steve Austin did everything in his power to make those people hate him, but all they did was grow to love him, and cheer him on. Then that whole Vince/Austin feud started, and blew up austin even bigger as a lovable heel. Then one day, Vince said, "Hey! I know a way to make these people hate you! Join sides with me!!", So, after all that time, they finally found a way to get steve austin over as a hateable heel, which was to join the one man he despised, the one man everyone despised. They could do this with john cena and Punk, or simply Cena and Lesnar, with Heyman in the back, managing this ruthless team of heels in the future. I don't know how it's all going to work out, i'm just saying, if WWE were SMART, they would take their baby face of the company, and turn him into a MEAN, RUTHLESS, HATEFUL full blown heel if they really wanted reactions from the crowd. Cena has the potential to be a great heel, much better than a baby face, thats for sure, but WWE has to give him that chance. I will admit, Dr. Thugonamics was a silly gimmick, but he got people to hate his guts, and thats what a heel does, now, maybe they can turn him into a more serious heel this time around, if not, then they shouldn't even bother trying, imo.