I don't like that idea. You have kid fans of Cena who will love him no matter how corny he gets and you have even more hardcore Rock fans who will love him no matter how much he craps all over the Mania main event and pretty much only shows up when it's convenient to him (Mania 28 is in Miami, Rock's hometown).
I mean, it's awesome. This is the type of crowd conflict the WWE LOVES. This is like Cena/RVD ONS heat. Cena, even admitted by Brian Alvarez (head smark) is really pretty good in the ring. He tells amazing stories, who cares about moveset, we aren't autistic are we? We don't enjoy "wrestle by numbers and do cool moves". We enjoy EMOTION, and STORYTELLING. People criticized his mania performance, but he seemed out of it. Probably due to knowing the Rock was going to bury the biggest match on the biggest show of the year. Other than that you can't tell me, unless you're an idiot move mark who has no idea of real ring psychology, that Cena hasn't been pretty great in the ring since about 2006. Telling great stories with a limited moveset is something both Rock and Cena do very well with limited movesets.
Personally I think Rock will do some more crappy movies and make sporadic appearances in LA, New York, maybe Miami. Cena will bust his ass and still get booed by guys who are worked into booing him and cheering by the kids who's parents buy his merch.
If you tag them, the Rock fans might resent Rock, or the WWE.
I have this idea to basically turn the Rock heel. Not like he cheats heel, but heel in the same way Cena is a heel to the people that boo him. Make the Rock exactly what Cena says he is (which he is). the ONLY time I want the Rock in an actual match is at Mania. Have Rock continue to preach via satellite how Team Bring It loves him and how he loves it and how "no callin yo momma" and fruity pebbles and homo jokes and catchphrases.
Eventually people will support Cena. Earning Cena respect (not universal cheers) is what this is all about.
WWE WANTS the older audience to boo Cena. That's waaaaay more unique and fun to watch than 80% strong cheers and 20% courtesy cheers. 100% of the audience is making as much noise one way or another as possible for Cena now. Why ruin that?
Edit:
Rock needs to work on his punches before he gets back in the ring for any sustained period of time; they look like terrible.