#1 Hollywood Cena

Cena's heel turn is possibly the second best thing in the wish list of the WWE Universe, only after CM Punk's return to WWE. Most probably both of these two are not going to happen in the near future, atleast inside a WWE ring.
Cena is now following the path of Dwayne "The Rock" Johnson and has now moved on to Hollywood, making sporadic appearances only on special occasions. John is going to lighten his schedule more as he slowly moves away from WWE and settles in Hollywood.
While it is impossible to imagine John Cena in any promotion other than WWE, it was the same for Hulk Hogan as well.
Hogan was the face of the WWE but once he drifted away from WWE and landed on WCW after a few movies, we witnessed the rise of WCW due to a notorious group known as NWO spearheaded by none other than Hollywood Hogan.
AEW would greatly benefit from bringing in John Cena, especially as a heel, if he ever wishes to come back to wrestling full time and do something different, even if it's for a shorter interval of time.