#4. Turn Roman Reigns Heel

Seth Rollins has already betrayed the Shield once. WWE is currently teasing Dean Ambrose to return the favor. So when the time comes to break the Shield again, a Roman Reigns heel turn can surprise everyone in the world and would allow Reigns to reinvent himself. The big dog is currently in a situation where he needs his Shield brothers to get cheered. He has been stale ever since he started his singles career. So a turn to the dark side would help him.
Turning heel has helped various superstars to get over with the crowd. The Rock, during his initial days, was greeted with "DIE ROCKY, DIE" chants by the WWE universe. However, a heel turn helped him to get over with the fans, and the rest is history. Even Bobby Lashley started doing well ever since he got his new mouthpiece Lio Rush and turned heel.
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In the longer run, the eventual face turn would give Reigns a proper babyface reaction.