I think Cena's heel run will be huge! But I don't know if it can be on the level of HHH's.
Maybe if he's given as much to work with, 'cause with HHH's heel run you really hated the guy.
I know a lot of people don't think cursing is a big deal and such, but Cena would have to be the complete opposite of what he is today.
And there would of course have to be historic feuds and battles in the ring.
We really don't get "battles" in the ring anymore (but that's for a different discussion)
It definitely will be one of the biggest turns in history, but I'm really interested to see how the run
Cena won't be turning heel any time soon. If at all. WWE has too much money invested in him as the face of the company. Bad for merch sales etc. Punk is a better heel and will continue to be the top heel for years to come.
And also, if the biggest face in the company turns heel who would he wrestle? There wouldn't be a wrestler that's as big of a face as he is to make it entertaining enough. And even if there was, after that person who would he wrestle after that? The WWE is light on legit face main-eventers at the moment so it would make no sense for them to change the biggest face in the company to a heel so they could face a lesser wrestler.
In before anyone says "OMG BUT HE CAN TOTALLY WRASSLE THE ROCK!1"
I think if Vince really let a heel Cena character go loose, he easily could. One of the main reasons Triple H was so hated during his times as a heel was not only because of his mic work and intensity that he brought to a feud as the "bad guy", but because he kept winning...most of the time cleanly. If they book Cena like that, and have him mow through opponents, he will catch major heat. I see now reason why it wouldn't work - and work in a big way.
I'm still of the opinion that a Cena heel run not only could happen, but will happen. I actually got a dissatisfaction vibe from McMahon's short appearance and I think it was because he realized that the kids don't bring the intensity. I see him shooting for the teenagers/young 20's crowd again, which is what they got in the Attitude Era. Adults actually bring more to wrestling than kids do. It's only been since the 1980's that wrestling was even considered a "kid's show". Before Hogan, it was standard adult entertainment.
In order for that to happen, you've got to turn Cena heel. Yes, he would be as over as HHH. I can actually see something of a double turn (Hart-Austin-style) with Cena and Punk. Think about all the times that Punk has pointed out all the little heelish things that Cena does. Meanwhile, with just a little tough-guy, understanding-guy thrown in, Punk could get uber-pops as a face (The IWC already adores the guy).