If u gonna make john cena heel, he gotta be in a heel stable al la hulk hogan.
His grip can be that hes tired of these new guys always stepping up to him wanting to take his spot, nobody can fill his shoes, look at roman. He will give his spot up when hes ready to give it up. But theres hope! These wrestlers(nxt call ups) stepped up to him looked him looked him in the eye and asked cena to teach them,show them the way and thats what he will do because when he finally call it quits one of these wrestlers will take his spot.