You should be blushing, Jack, because you're the one who generally rips into someone who suggests that Cena may be turning heel.

However, so am I, and I couldn't help but think the same thing. Wyatt's promo was
that good.
But that got me for all of an hour and a half, as while the fans voted for the 3 on 1 match, I think the reason so was for the intrigue of how the match would play out, not that they wanted to see Cena get killed. It was certainly a pro-Cena crowd, I thought, and this was never better illustrated then when Cena hit the AA on Bray Wyatt, and the crowd absolutely erupted. There were also some singing along with him as he sang "He's got the whole world in his hands", but the majority seemed to be pro-Cena.
As for a turn? There's the usual drawbacks, such as can WWE truly afford to lose two of their top three faces, turning Cena, and losing Punk? A heel character will likely be detrimental to his merchandise sales amongst kids, women, and those male adults who love him in his current role. The same doubts that there always are, in other words.
But here, I think that they're at least open to the possibility. This is a feud that likely won't end until Payback, so they've got time to decide. And I think how they'll go about it is based on crowd reaction to Cena's character. Yes, he was the smarmy, cutesy character that make people hate him two weeks ago, but he tied it back around as to why he does it. Bray plays mind games, those are Cena's. But when Cena is serious, there are none better. His promo on Raw reinforced this. Cena can cut as serious a promo as anyone in the business.
So, I think it's how they book him and that storyline from here on out that will determine what they decide to do with him. If he's booked as "The only guy in the room who thinks his routine is funny", I think we could see a frustrated Cena losing fans because of it, and eventually succumbing to the monster.
Of course, it;s 's the battle between what's best for the product against what's best for profit. Cena is due a heel turn, anyone playing (close to) the same character for almost ten years is. But that would obviously diminish his merchandise sales and his Make-A-Wish and other ambassador duties, which hurts the business aspect of things.
I could see them doing a quick heel turn, but nothing long term. Something to give what about half the crowd has been clamoring for, "satisfying them", then turning him face once against. His character would likely be much different at that point, so it could be a very good thing should it happens.
Right now, for the first in some in time, I'm not sure. And I like that.