#4 The spot for the top heel is open
WWE is in dire need of top heels. The company hardly boasts of any credible main event villains today. Superstars like Edge, CM Punk, and Chris Jericho made a name for themselves by portraying a heel character to perfection.
Sure, stars like Kevin Owens and The Miz are great as heels, but they are upper mid carders who are occasionally brought up to the main event level. John Cena is anyway booed out of the arena everytime he steps into the ring. A heel turn will justify those boos and set him up as the topmost villain of WWE.
With Brock Lesnar rumored to leave WWE and Samoa Joe still sidelined due to injury, a heel John Cena can easily feud with top babyfaces like Finn Balor and Seth Rollins and elevate them to become future superstars, or even challenge and win his #17 World title.