Back to the 2011 Royal Rumble (and the WrestleMania implications), Alberto Del Rio's win was a great one. Smackdown, again, is in DIRE need of main-event heels. Every time they get one, he gets jacked and sent to RAW.
Edge was the alpha heel for years. But, now he's a face. Jericho is still gone (they moved him to RAW, first by putting the tag titles on him, so he could be on both shows).
Since 'Taker won't be in the main event and there's no scintilating beef among the non-champions, one of the world title matches should be the main event
With the likelihood of a heel winning the main event being low, I'd say the WWE title match will be the feature bout. Miz will lose the title at 'Mania, likely to Cena but PERHAPS to Morrison.
That is, UNLESS they let Edge beat Del Rio. I'm sure Edge is tired of losing at Wrestlemania (he's dropped three straight title matches).