I'm pretty sure most of the MLP crowd wasn't going to see Insidious 4 hahaha but yes. Split and Get Out showed that horror/genre films can do well outside their normal season.
I mean that, in the grander term.
September and October, will have a lot of films, but they don't have nearly as many family films for them to watch while the Suspense/Horror scene takes full stage.
Outside of The Lego Ninjago Film and My Little Pony, it is crowded with many films in those two months that are more catered towards an older demographic, than there are for kids and families.
I believe Insidious may of been just due to the success of Split, and I wouldn't be a damn bit surprised if that is the reason, and that I don't think with a delay in the film; it means that it won't happen.
Insidious, has been a tested franchise, that has been responded on well when it comes to Horror Nights (with Universal Hollywood going for three if their leaked line-up stands to reason), and that if it's a shared; it would be the second time that Orlando would have the ability to bring the franchise.
And, I have my own doubts, and believe that it will not be a best of, and that it will act more similar to The Wolfman in many way's, giving a somewhat tease of what to expect while also bringing an IP like that to the parks.
Unless, if Hollywood's is primarily exclusive, then that'd be something else.
And to bring up the film side, I think Saw may move up; with Insidious taking the dip to January.