Even though H2018 is now out of the question, what about Halloween 5? Back when they announced Halloween 4 Murdy mentioned something along the lines about wanting to continue the storyline of Michael and I think H5 is the last movie that can be done without worrying about IP-related issues, as i think Dimension owned the rights for H6 and forward.
To be clear, I'm under the impression that several of the Michael Myers sequels are still available for potential use. It's the original Halloween and the reboot that are off limits. Universal also has a claim to Michael Myers himself thanks to Halloween II (which they have a stake in), hence his continued appearance in the Special Effects Show; they could, if they so desired, pursue an original take on the character so long as it didn't skew too close to Halloween or the reboot (which is... tricky). It's how they're able to continue using Chucky despite MGM's claim on the original film; it's also why almost all Chucky merchandise is branded as "Child's Play 2" (i.e. Universal's film) in the fine print.
As far as canon - look, we did Halloween 4 in a year where that plot was explicitly rendered moot. They care about Michael Myers on the poster more than anything else.
I otherwise tend to agree with Freak's assessment that something is going to need to give. For now, the Insidious film franchise is done - Leigh isn't interested in making more, though I suppose they could pursue sequels without him (though I don't believe any are imminent). Unfortunately, we're probably going to see more Purge, either in the form of the next sequel (which is absolutely happening) or the ongoing television series. The lawsuit concerning creative authorship could potentially impact those efforts, but for now, the siren will continue to ring.
Happy Death Day seems like an obvious choice for a maze. I would expect it next year.
I also wouldn't rule out (deep breath) a CryptTV attraction, whether it be a scare zone (perhaps the Gauntlet) or one of the smaller maze venues. Blumhouse has invested in the company and through Universal has a deep relationship with its content slate, with the shorts appearing on the Terror Tram and on screens in the Metro Sets; it's extremely popular amongst tweens (a demographic Universal continues to court with Stranger Things), so it's absolutely not out of the question.
Monsters cost a lot of money. I would expect that maze to return, in a new reconfigured location, with additional characters (Creature from the Black Lagoon, Nosferatu) and other changes (probably fewer Phantoms and an actual scare for Bride).
Stranger Things Season 2 is a given, though I'm deeply curious how Hollywood intends to execute a maze so dependent on puppets; AWIL was pretty hit or miss, and this maze needs to be a slam dunk.