#2 Ambrose turns heel
Well this is one of the most logical outcomes right now. The Lunatic Fringe turning on his brothers has been so heavily implied that everyone is expecting a Shield break-up due to Ambrose. The announcers are hinting at it, and that's one of the major reasons why this could really really come true.
It would make sense in a way. Rollins is the IC Champion, and the Universal title isn't going away from Reigns' shoulder anytime soon. This leaves Ambrose in a limbo. You can have your top star only for so long without a title. How are you supposed to root for someone who doesn't hold the gold or demand it?
If Ambrose turns heel, he could feud with Rollins for his IC title, or move to the blue brand to reclaim the United States Championship.