Another awesome Mania idea....Brock wins the title at Elimination Chamber (either in a chamber match - which would be awesome, since Brock in a chamber would be pure destruction - or in Brock/Cena or Brock/Orton (they could really do both despite Brock and Orton both being heels) and then Bryan vs Brock at Wrestlemania. In this scenario Bryan breaks free from Wyatt during the Royal Rumble and betrays him to win.
WM30 could be amazing honestly with the assortment of guys they have. last year they had Lesnar, HHH, Punk, Taker, Cena, and Rock. They lost Rock, but Orton has become more important now, Bryan has become more important now, and Batista is coming back as well. HHH is also in a better role, and then we have Bray Wyatt as a wildcard and if they want Sheamus can be inserted into the main event. There's a lot of ways they can take the card. Maybe they can even get HBK to wrestle, though it's doubtful, but HBK/Punk or HBK/Bryan would be amazing
Edit: Plus an outside chance of Roman Reigns getting a breakout star push