It isn't just that a Reigns / Cena feud offers a main event for WrestleMania 32, it offers a main event for WrestleMania 33 as well. It seems natural that a rematch should take place, just like Cena did with The Rock a few years ago. The story would be that Reigns defeated Cena at Mania 32, leading to Cena coming back for revenge the next year. It would be a bit like Shawn Michaels going after The Undertaker two years in a row, "I know I can beat you." But ultimately, this would just be the final part of putting Reigns over in the most major way possible. Just like WrestleMania 32, he defeats Cena at WrestleMania 33. The torch is well and truly passed.