I hope hope hope Kane will not turn heel. In that environment, with those superstars around him it can only end up being awful. I do not want to see Psycho-Kane return only to see him job to Cena, 'Tista or even Mystery-o.
Batista could be a very interesting heel. He has scraped heel-ness on several feuds in the past, what with being that whiny bitch when Michaels retired Flair, acting as "Mr. Thousand Title Shots" on several occasions and so on. Why not try an honest, real heel run where he could just be a dick all around and back it up, too.
Also we could have an Evil Evolution once Orton returns.
If Punk turns heel he should have a partner. Preferably Y2J. That would be good.
I can not see Rey turn heel, ever. The only part he can fill out believably in the WWE of this age is the part of the underdog. And evil underdogs are kinda boring.