Jesus Christ Superstar. OK, DCnDC suggested “ET 2: The Revenge” already, but I’m not (entirely) just riffing off that.
My daughter and I saw JCS on stage a few years ago (it’s SUCH a great political story, and good music–we ignored the religious aspects) and afterward she tried to convince her aunt that they did the “alternate ending”…
Spaceballs, naturally.
Well, with that cast, sure, but “never give up the ship”.
They made several sequels.
No, they didn’t.
An old joke doesnt get any better for repeating it over and over. 
By Grabthar’s hammer - no one has mentioned ‘Galaxy Quest’?!?
Fast Times at Ridgemont High, Class Reunion.
We need the third Sicario movie.
Sons of Three Amigos!
I thought the original Galaxy Quest wrapped things up pretty well, but maybe there is room for a sequel. At then end, isn’t the fictional “Galaxy Quest” TV series revived? Imagine the cast members making that new series while knowing that there’s an alien culture watching and mimicking their every move. Lowly actors might try to dictate what happened on the show, although they couldn’t tell anyone why.
It wouldn’t be the same without Alan Rickman, though.
The Breakfast Club Reunion could be interesting…
The Usual Suspects. There’s gotta be a Kyser Sose story to be told.
You know, I always (personal head canon) considered Gross Pointe Blank to be a fun sequel to any number of 80s high school comedies, not just a spiritual sequel (in some interpretations) of Say Anything.
John Cusack has said in interviews that War, Inc. is a spiritual sequel to Gross Point Blank.
A Breakfast Club reunion would be good, too.
It doesn’t need a sequel, because it’s just about perfect in and of itself, but I’d love to see American Hustle, Part 2. The triangle of Irving (Christian Bale), Rosalyn (Jennifer Lawrence) and Sydney (Amy Adams) were so much fun I’d be happy to spend another couple of hours watching what they get up to once they’ve finished their respective prison sentences.
He was just found not guilty
Yes, the greatest trick the Devil ever played was convincing the jury to let him off.
A world war Z style sequel to invasion of the body snatchers could be interesting.
Wait, what? Was this supposed to be a sequel to the one with Ron Ely back in the 70s?
(I keep hearing rumors about a Doc Savage movie with Dwayne The Rock Johnson but I expect that it will never happen.)
Who Framed Roger Rabbit was a Hollywood adaptation that the original author liked so much he scrapped his original story as a dream and wrote a sequel to the film’s plot. I feel we deserve to see that and everyone would be happier.