The Rock at The Elimination Chamber
My guess is that they are working their way backwards from Wrestlmania 30.
Rock(c) v Cena at Wrestlemania 29. Cena heel turn.
Then at Wrestlemania 30:
Heel Cena v Taker
Brock Lesnar v The Rock -perhaps his last match as there is not that many megastars left to face and he could go out on a high since it's Lesnar, and I doubt the fans would shit on them like Lesnar/Goldberg, because let's face it, it's The Rock.
There's your biggest Wrestlemania of all time, or I could be just talking a load of shit, in which case, ignore this :Rock