It seems like they will let the rights go for the right price. They haven't exactly been choosy lately.
I wouldn't mind any of these. LotR might be a bit redundant with some of the other fantasy properties represented. Star Trek presents some unique challenges with all of the different interpretations. I'm sure it could be done, but there are some difficult choices to make so you don't wind up with a less popular Galaxy's Edge. BTTF is only relevant to us old folks. I like it, but I think the current representation (vehicles, merch and meet and greet) are the appropriate level.
I'll throw out some ideas:
Jaws
James Bond
Ghostbusters
Dr. Who
Beetlejuice