Okay. Whoever keeps suggesting Treehouse of Horror, stop. That makes so little sense and runs so contrary to the rest of the HHN "brand" and target audience. I don't think a Treehouse of Horror event of some sort is out of the question, but it'll be a daytime overlay of the new additions, not an HHN house. Let's think reasonably here.
I don't think a 2 park event is completely out of the question at this point. I'm not saying it's likely, but it's worth considering. The crowd control was better this year, but they're still clearly choked for space. Expanding out to Toon Lagoon (for the B&T stage) and including the marvel rides would do much to alleviate a lot of the traffic concerns...
If I were a reasonable decision maker for HHN, I'd say that the event has grown to require a 9th house. This won't happen, as we barely got enough budget for the 8 we had this year. (Seriously, La Llorona was a blatant retread of Catacombs & Forsaken, while Afterlife was the biggest joke of an HHN house I've ever experienced, and I went through The Spawning.)
If we had to guess about what properties we'll inevitably get? American Horror Story seems likely. I wish they'd do Murderhouse, but for marketing purposes they'll probably just do Coven, which is fine but whatever. I would expect at least one movie tie-in (isn't Sinister a Universal film, and isn't that getting a sequel next year? I could see it). I'd expect at least one Hollywood hand-me-down, so either Insidious, El Cucuy, or both. Walking Dead... I'd like to say no. Not enough variation in the new season, they'd be really reaching for material... but marketing could twist creative's arm and force them to turn out a shoddy product (again).
I hope they're done with video game houses, but it really doesn't seem like they are (even though they've demonstrated they can't pull them off at all) - so I'd expect Dead Space or another property of a similar pedigree.