I'm pretty sure neither of those franchises are capable of having ten good movies.
So you wouldn't put a limit on Finding Nemo sequels or Ender's Game sequels or anything? There's absolutely no story you can think of that can say all it has to say in 3 films?
And are there no movies you like that didn't get a sequel? They don't deserve a trilogy because they deserve infinite films?
And if a story has been told great once... like Back to the Future, should it ever be rebooted? Should that have gotten infinite sequels too?
I have no clue how many Ender's Game novels there are...or if the story is left open to explore more of the universe. Haven't seen the movie either, so I don't care if there is a trilogy. If the universe is as vast as Star Trek or Star Wars, then I see no reason why it couldn't continue. I also have never seen Finding Nemo, so not only do I not want a trilogy, I didn't watch the sequel. As far as Back to the Future goes...boy, I really didn't enjoy the sequel and found it unnecessary, and never watched the third one.
However...I'll play your game because I realize that it's just for fun...
There was a movie called Upside Down last year...a fantasy/sci-fi film about a world where another world was on top of it...so you look up and see the tops of their skyscrapers (and gravity is reversed). The movie rushed through DECADES of story, dealing with lost love, the exploitation of the poor by corporations etc. It was WAY too much for one movie.
So...
Upside Down 1: Tell the back story about the world, set up the scenario where the corporation that controls. The two leads are kids, and they meet and become close but are kept apart by the rising tensions. The main thrust of the story is how the under world is being exploited by the corporation.
Upside Down 2: Now teenagers, the two leads try to get back in touch, but can't. He is leading a life of poverty while she takes a job at the corporation. In this movie is where the under world becomes a wasteland and the stuff that he explains happened to his family goes down etc. It's also where armed guards take control of the space between worlds.
Upside Down 3: As adults, she is a top executive...and he has hatched a plan to get to the top world and bring it down. The rest of the actual movie happens.
Basically, I'd get more involved in the world, and spread the main story out over 3 films instead of cramming it all into one (which ruined it).