Dolph Ziggler IS the WM Main Event
Creative would never do this, but picture if Dolph Ziggler was in both championship matches at Wrestlemaina. He wins the Rumble and decides to go after the WWE championship, but he also has his MITB briefcase and announces that he's going to cash in at Wrestlemania.
Superstars have announced beforehand when they plan to cash it in (RVD, Cena). And Ziggler has been known to pull double duty at pay-per-views before. And financially speaking, that would be a big payoff and a great way to sell Wrestlemania. Never before has one superstar challenged for both titles on the grandest stage of them all.