Given how much of an absolute fucking terminator BRAUN has been built as, the 50/50 finish to the Braun/Reigns ambulance match, Reigns declaring himself the #1 contender for Summerslam a while ago, and Joe looking like he's not finished yet, I feel like any of these are possible.
Lesnar vs Braun is something I want to see, but it still doesn't seem like Braun is finished with Roman, so that could pose a problem if Reigns wants Lesnar. So we could be looking at rematches at Summerslam.
A four-way between these guys would likely destroy the planet, so there's some risk there.