#1 Probably will: Seth Rollins
There's a solid argument to be made that Seth Rollins has already main-evented The Show of Shows when he cashed in his Money in the Bank contract at WrestleMania 31. But give it time and it seems it won't be long until the former Universal Champion one day headlines the event with a match he doesn't have to crash.
A fixture of the main roster for the past seven years, Rollins has always been booked well, whether as part of The Shield, The Authority, WWE World Champion, feuding with Triple H, or most recently taking on the Beast Brock Lesnar. This plan has garnered the Architect a legion of fans, and if he remains injury-free, it seems Rollins has a lengthy WWE tenure ahead of him, one that will include a Mania main event.