As someone who is older than 15 years old, I wouldn't mind seeing Cena turn heel, so long as they repackage him.
But, I have to admit, WWE is utilizing Cena perfectly right now. WWE needs someone like Cena to market towards the younger audience and he's playing the part of the "straight edge" face well too. To turn him heel at this point just wouldn't make any sense as he's not exactly the most over in the company, but he's over enough in his current incarnation. He's in a "comfortable" spot. So, to turn him at this point would be a waste. But when (not if) it happens, it'd be a time where it would make the most impact for not only himself, his character, but for WWE as well. Right now, too premature. And again, Vince is deternined to put Cena over with the kids and everyone's enjoying his current merchandise sales. Beneficial for Cena to turn heel? Verdict: Not now.
Triple H as face or heel is just burned out in either role. If HHH turned heel tomorrow, it would have minimal impact on anything. He's played out both roles for so long that there's no intrigue either way. It's comparable to if he decided to stop wearing black boots and started wearing navy blue boots. Yeah, there's a bit of a difference, but, in the end, it wouldn't really matter. Turning on Shawn Micheals. It gives me a "been there done that" feeling. HHH turning heel on most of the Raw or Smackdown roster really doesn't interest me at all. He's danced with everyone who matters right now. They'd REALLY would have to come up with an incredible storyline to make it interesting or intriguing. And I have ZERO faith in WWE "Creative" to come anywhere close to that challenge. HHH Heel Turn Beneficial? Verdict: Wouldn't matter either way.
That leaves Batista. Personally, I think ANY interest in Batista peaked when he was "dumped by Evolution." It's really been downhill from that point and I don't really see anyone really caring that much about Batista in his current incarnation. A heel turn with some repackaging wouldn't be a bad thing for him. The challenge however, would make people care about him again. Batista heel turn beneficial? Verdict: Yes... but would any care?