Aside from a turn making no sense from a business stand point, I also don't think it makes sense from the stand point that a heel Cena was actually pretty terrible to be honest. Mind you I'm old school and prefer my heels making me want to legitimately hate them, not repeating their catch phrases or laughing at their raps. I just always felt Cena never had it in him to be a real true heel. If it didn't work 10 years ago why would anyone think it would work today?
He's not turning heel. Although you are objectively wrong if you think that the Doctor of Thuganomics wasn't awesome. Cena's promo work on Monday and in previous times shows that if he wanted to be a true heel, he would RULE. Hell, look up a clip of his OCD behavior with Nikki on Total Divas, where he's apparently a condescending dick. That character, the corporate musclehead stooge super-jock who never let go of the high school pecking order, would be PERFECT for him.