So what movie sequel (or even a remake) do you think would make the most money? Obviously I realize money doesn't equal best movie, but the question is just about money.
I would call the following list shameless cash grabs. I'm not assessing if a good story can be fully mined out from these IPs, but you wanted it strictly about box office and money making potential.
1) Harry Potter Part 8 - Bring back the original three kids as adults in a stand alone story. Will get boycotted because of JK Rowling, but the franchise is basically a money printing machine.
2) Iron Man 4 - Bring back RDJ in a stand alone story that happens pre Infinity War
2A) Iron Man 5 - Lay the seeds to Tom Cruise inheriting the mantle of Iron Man from Iron Man 4. This would be a post End Game story.
3) Avengers 2.5 - Bring back all original Avengers for a stand alone story between Age Of Ultron and Infinity War
4) LOTR Epilogue - In the actual books, the original surviving fellowship spent months together in the outdoors, because they knew their friendship would have to part and likely permanently. Bring back Peter Jackson and put them in a stand alone adventure. I get that everyone is too old now, but it would be a money making machine anyway.
5) The Godfather Part 4 - Leonardo DiCaprio was approached 15-20 years ago to see if he would play young Sonny Corleone. So put in Robert DeNiro as aging Vito Corleone, who is older but not as old as Brando was in the timeline. Use Al Pacino and Andy Garcia in flash forwards for cameos. Build the movie around Sonny, let Scorsese direct it. Use Joe Pesci as the main enemy/antagonist.
6) Interstellar Part 2 - This film has a huge cult following. Christopher Nolan has his own cult following. Astronaut Rust Cohle and the mind numbing actress who shall not be named carry enough star power to carry a film. There is also enough set up at the end of the original to create a sequel. What's interesting is you can bring back Timothee Chalamet in some fashion to replay the role of the son, because that will cash in on his ability to drag in the teen audience/women and cash in on the Dune hype.
7) Alien 3/Colonial Marines - Just let James Cameron do a sequel to Aliens. Call Alien 3 a dream sequence while Ripley was in Cryo Sleep and wipe out all the other movies from the canon. Bring back Sigourey Weaver and Michael Biehn as older versions of their characters. In charge of a lot of Colonial Marines. Have them invade the Aliens homeworld. Make it a full on war/siege.
8) Predator 3 - Wipe out all films after Predator 2 from canon and the timeline. Have Arnie return as Dutch. Have the ship from the end of Predator 2 ( There were 7-8 Predators in that scene) capture Dutch. Have the entire movie about Dutch trying to escape the ship in space while fighting multiple Predators. Change the format. Now Dutch has to hunt them while trying to find the escape shuttle. Make it essentially like System Shock 2 in spirit. Bring back Danny Glover and Adam Baldwin in cameos.
9) Tropic Thunder 2: The Les Grossman Story - Bring back Tom Cruise as Les Grossman and spend the entire movie with him. Full on satire/comedy. You can bring back the original Tropic cast in supporting parts.