With 28 in the history books, and considering everything that's going on in the park, I have a feeling this'll be a very interesting period of speculation!
As what with everyone is saying, I'm expecting more nights, houses and hopefully shows to try and combat the crowds. For the houses, I'm hoping for another evenish split of IP/Originals like this year.
As for the IP's...
Stranger Things Season 2 is pretty much the no-brainer of them all, Netflix adored Orlando's version, so it would be very understandable they'd want to ride that train again.
KKfoS has a good chance due to the general good reception by everyone and the fact we all know the creative team would love to do more with it.
Everything beyond that is more up in the air, though I will say I'd love to have a Hellraiser house. That would be ripe for the creative team to put some original spins on.
Other then that, I think the most interesting thing to discuss for next year is what house/queue locations are we gonna' have? If Kidzone finally goes under construction, that could throw things out of whack for the parade warehouse queues, maybe even the original warehouse. An what happens if Shrek 4D finally closes and goes down? That's a loss of a house venue right there. What if FFL finally goes down, too? There goes a venue for a show. Add in the rumor of them looking at 12 houses, and now we gotta' figure out what nook and cranny they can be squeezed into.