I think WWE's focus is to get the Miz extremely over as a heel to set up a Championship match at Mania w/ CM Punk.
The Rock/Cena match doesn't need a title in it, and a Miz & Punk one on one program would probably fit the bill.
I know a Heel H, SCSA, or Y2J is what folks want, but if all of those fall through, I can see an over heel Miz vs Punk being a great co-main event at WM, especially the promos and mic work leading up to it.
You can make it like The Miz is Mcmahon/Laurinaitis's chosen champion, conspiracy, and that's when Punk makes the save and beats him @ WM. establishing himself as a mega top face.