over all this didn't stray too far from for them still continuing the original story...
a, Lost in Scaradise, type movie could still work
tho, I think the next logically step would be to go back to Monsters University {introducing a new generation of young monsters}
but, this time it would be a reverse take on the social hierarchy on campus (from Mike's and Sulley days) where it would now be a Comedy Collage, with the monster's previously deemed too small/weak/silly to be "scariers" being the Big Monstars on campus, and the biggest/scarest monsters struggling
we've already seen set up for Mike to be a professor at the school, with his little stint of "Mike's Comedy Class"(maybe they get to the point where they've trained enough Jokesters to effetely run the laugh floor, that Mike is ably to retire and take a teaching job full time)
at first, Mike kinda see's the humor in the ironic twist of faint on campus (remembering his days in school) an always takes the funnier monsters side, turning a blind eye (no pun intended) to them harassing/bullying of the bigger monsters.... even occasionally joining in on poking fun at the "scary monsters" who aren't funny himself
until Sulley, comes to visit him on campus and see's this happening, and tells Mike how wrong it is... then Mike and Sulley team up to reach out too/help the scary monsters be funnier (or find other talents of theirs) teaching them they can be more them just scary....
I mean it basically writes itself (an yes I'm aware that I put way too much thought into this lol)