The chief reason for Punk coming back would be to have him one hit beat Seth Rollins (shipping him off to Smackdown in the process) and then trashing the AEW belt he's been carrying around and shit talking Roman and declaring the Raw participation belt the only one that matters, insert shoot comment that Roman only keeps the belt because he keeps lying that he can get Rock back full time.
Putting the belt on CM Punk would make the Raw belt actually mean something, especially if you go the angle of allowing Punk to shit talk Roman and when Roman finally does come back, find out he's curtain jerking the opening match of the Royal Rumble, denied a dressing room, being forced out the arena at gunpoint by security afterwards, and generally speaking being treated like dogshit along with Heyman, who gets banned from Raw because Punk doesn't want to deal with his parasitic bullshit.
Make Punk a tweener who's egomaniacle but meaning well and just have him troll Roman until Mania and beat him/unify all the belts THEN do a fuck-up finish with Cody which ends with Cody getting one belt and Punk the other. Cody gets Smackdown, Punk Raw, and you toss the Usos and Solo into a garbage truck with Roman and we never see them again.