Let's say Punk keeps the title at Royal Rumble. I don't think he would drop it at the Chamber PPV so he might as well keep it to WrestleMania. So who should Punk drop the title to? I'm sure the people who had a problem with Rock winning the championship would also have a problem with Undertaker winning the championship as well. I have heard people talk about a Rock/Cena/Punk triple threat scenario but if Rock's in a title match at Mania he might as well go in as champion if that's the case.
That is totally worst case scenario. I don't even want to imagine a triple threat match...god no.
Best case scenario:
Punk wins via Lesnar's interference (seeting up Rock/Lesnar at 'Mania)
Why is this the best case?
Simple, the two part timers have a match that in no way knocks the normal roster guys around. It also doesn't matter who wins or who loses because neither will be in the ring again any time soon after. Its a fresh match and It'll also make Vinnie Mac a couple dollars in the process.
It also gives Punk huge bragging rights that his character can use during the RTWM leading up to him ultimately dropping the strap to either the Rumble winner or the elimination chamber winner.
What about Undertaker & John Cena?
No idea. I definitely expect Taker to call for Lesnar because that's a match he wanted for a loooooooooong time. Of course this effects my original idea (Brock/Rock) but this is a second best scenario.
Undertaker vs anyone else doesn't make sense, unless The Rock challenges the streak (which would be mind blowing but highly unlikely).
John Cena is an anomaly. He's wrestled all these guys, with the exception of Undertaker, recently. Second worst case scenario brings us Rock/Cena II which puts the title on Rock who disappears for two months to drop the strap to Cena. That's no problem to Vince of course, but to a lot of us its a HUGE *UGH* and of course it de-rails Punk entirely and Punk can do more with the title than Rock or Cena can at the moment.
Okay so you don't want Rock/Cena II but you need Cena in a main event and no other match will matter or make sense...that leaves the triple threat idea...