I remember when that happen but I've been reading that they're okay with not giving Cena the title to go against Dwayne. Having the title on Cena is kinda pointless when they can keep the title on someone else to have a high profile match I.E Punk/Jericho.
Rock/Cena is going to be an epic match, but both ways I look at it I see that Cena has to win, heel or face. This is supposed to be a passing of the torch and having rock win wouldn't accomplish that (though it would be awesome) And while I agree that Cena should be a heel for all the reasons you said, I can't see them doing it due to the fact that it doesn't look like they truly trust Punk as taking over the role of top face