I mean, if we're just going by "relatively well known" properties, there's still quite a few cool horror IPs they haven't done at all, or at least for a very long time: Tales from the Crypt, Hannibal/SoTL, 28 Days Later, other Stephen King stuff like Castle Rock, The Descent, Fright Night, TWIN PEAKS, Re-Animator, Eraserhead, Suspiria, horror video games like Bloodborne, the Last of Us, Dead Space, the new Resident Evil... I mean, hell, we just spent two pages posting horror comedies they haven't done yet. Where's our Dead-Alive or Killer Klownz maze?
That's to say nothing of what new IPs are coming in the future. Stranger Things came out less than 2 years ago. Insidious turned into one of the biggest horror franchises out there after 4 short years, ditto with the Purge. Who knows what the next big thing is gonna be?
Now, does that mean we should/will get all of these different mazes? Well...probably not. There are rights issues, issues of financial feasibility, issues of practicality, issues of whether or not the GA knows what these properties are... At some point or another, it makes sense to add some new, original themes, especially if they eventually up the house count to 8 or 9. But I don't really foresee a shortage in IPs. There's just too many out there and too many coming soon.
Edit: Almost forgot about Candyman, Phantasm...hell, we haven't had a proper Child's Play maze yet! Terror Trams, HoH reduxes, Scare Zones, but never a real maze.