#5 Fastlane -- Betrayed faster than the speed of light
Despite having commenced a new feud with either Braun Strowman or Drew McIntyre, John Cena would be remiss to overlook his former rival, that being either Seth Rollins or Elias, with whom he'd have gone 1-1 at TLC and the Royal Rumble respectively. That naivete is exactly what will allow Rollins/Elias to strike when Cena thinks their feud is already done with!
With that in mind, when Cena faces Strowman or McIntyre in a singles match at WWE's Fastlane PPV in March of 2019, the WWE could have Rollins/Elias cost Cena the match by way of outside interference -- subsequently rekindling the feud with Cena. Bear in mind though, although the Fastlane match would logically end by way of Disqualification, it's extremely important that Cena makes Strowman/McIntyre look strong throughout the match at Fastlane.
Moreover, after being attacked by Rollins/Elias, Cena could then embark on the road to redemption, albeit not in typical Cena fashion, but in a vastly different manner...