Scott,
Wouldn't the obvious feud to build to for WrestleMania 32, be Roman Reigns vs. The Rock. Reigns could go uber heel, blame the fans AND Rock for not supporting him, and dominantly plow through faces (including a Brock-style destroying of Cena at Summerslam), win the title mid year and lose it when Rock shows up to defend his and his family's honor. BOOM: WrestleMania match. That, plus Sting/Taker retirement is a pretty good double headliner. Throw in Brock/Bryan as an apology to the fans and Dallas has a Hell of a Show!
Dude, they need to sell ONE HUNDRED THOUSAND tickets for that show. Roman Reigns ain't gonna be anywhere near that main event. Put the names of Brock Lesnar, The Rock, HHH, John Cena, Undertaker and maybe even Shawn Michaels if you're desperate into a hat, pull out any combination of three matches with them, and that's your main card. Even then, I dunno.