I have a hunch though, that if the story doesn't live up to the first 3, they will just make it Direct To DVD.
There's been so many Disney releases that were supposed to be released to theatres and ended up Direct To DVD instead after the audience testing said it wasn't up to scratch.
Pixar have been through the rough since Cars 2, so they need to make sure they tread lightly before making the same mistake. A sequel that didn't need to exist.