I'd probably prefer a Rock/Punk/Cena triple threat over ONCE IN A LIFETIME...AGAIN. Adds a new dimension to the match, and gives Punk something to do.
In fact, I'm going to do a quick Wrestlemania card (in order of how it comes into my head, not the order I expect it to actually happen in).
WWE Championship: The Rock (c) vs. CM Punk vs. John Cena
World Heavyweight Championship: Alberto Del Rio (c) vs. Jack Swagger
World Heavyweight Championship: Alberto Del Rio (c) vs. Dolph Ziggler
Daniel Bryan vs. Kane
Tag Team Championships: Brodus Clay/Tensai vs. Prime Time Players vs. Team Rhodes Scholars
The Shield vs. Ryback, Sheamus & Randy Orton
United States Championship: Antonio Cesaro vs. The Miz
Intercontinental Championship: Wade Barrett vs. Bo Dallas
Brock Lesnar w/Paul Heyman vs. Triple H w/Vince McMahon
Big Show vs. Booker T
In terms of big(ish) names, that's leaving out Jericho, Mark Henry, Christian, Sin Cara, Rey Mysterio, and Undertaker. Everyone else can just go into the usual battle royal. Suppose Sin and Rey could go in the tag titles match, if they're healthy. Christian may have to wait until after Wrestlemania to return, and I'm not sure Taker is up to it. So Jericho and Mark? I suppose they could face each other, but it'd be a bit of a throwaway match/feud, and I'd like them to have something more substantial.
Edit: Shit, divas. Erm, big tag match? Layla & Kaitlyn & Natalya vs. AJ & Rosa & Tamina?