The main event will be an Elimination Chamber match for the WWE World Heavyweight Championship between Randy Orton, Brock Lesnar, John Cena, Sheamus, Daniel Bryan and a sixth man. Since four contenders have already been announced and since Maddox (or The Authority) will obviously put Lesnar into the match within the coming weeks, then the sixth man will probably earn the golden opportunity to compete for the WWEWHC in the "biggest elimination chamber match in history" by winning a battle royal or something. Just throw in Kofi or some other midcarder who could use a rub by being in a match of this magnitude.
The match basically goes like this - Lesnar starts off and at some point eliminates whoever this sixth man is. The Wyatts interfere and cost Cena the match, and maybe Lesnar gets credit for that elimination, too. Then everyone left (Orton, Bryan, Sheamus) gangs up on Lesnar and hits their finishers and whatnot and eliminates him. Bryan then eliminates Sheamus, and maybe Sheamus is so pissed about it that he Brogue Kicks Bryan before exiting the chamber. This wouldn't be a complete heel turn just yet, but it'd be the start of it. Orton then picks up the pieces and finishes Bryan off to win his first ever chamber match.
All of this sets up several programs that are all rumored to happen at Wrestlemania - Orton/Batista, Lesnar/Undertaker (Lesnar goes ape shit after the loss and targets Undertaker's streak since it's the next best thing to winning the WWEWHC), Cena/Wyatt, Bryan/Sheamus.
Batista vs Del Rio - ADR will probably challenge Batista to put his Wrestlemania title shot on the line, and whether he does or not, this will basically be a squash match on Batista's part.
The Shield vs The Wyatts - The Wyatts win, establishing themselves as the meanest and baddest group in the WWE. And it'll be pretty much the last straw for The Shield before they break apart (I don't expect it to happen at the PPV but maybe on Raw the next night.)
Punk vs Kane - Punk defeats Kane, further building towards his confrontation with Triple H. Nothing else to this one, really.
The rest of the card, who knows.