The problem with a LOR park is that Disney would have to borrow the rights from New Line Cinema which may be hard to get since it's been a money making machine for the company, but it could definitely work.
If there were to be a 5th park I think that you would have to look at the what the theme of the parks are first, and see what they are targeted at to compete with.
MK- Fantasy/Fiction/A little bit of everything
Epcot - The Present/Future/Education
Disney Studios - Movie and TV making history; aimed to compete with Universal Studios
Animal Kingdom - Animals/Ecology; aimed to compete with Busch Gardens
The next logical step may seem to be to go after Sea World, which would make very logical sense if they were planning on not revamping the Living Seas and eventually transporting all the animals into a WDW Seas park. The only problem is, is that the park would fit in perfectly as a land in AK. The problem with WDW is that it would be very hard to make a 5th park because they have so many minor parks that have themes:
Wide World of Sports - Sports
DisneyQuest - Technology
BB/TL/RC(if it's still open) - Water Parks
The one theme that they have yet to tap into which may be an awesome theme is something like The Ancient World, and have lands like Egypt, Rome, Greece, Vikings, Native Americans, Mongolia, Atlantis?:drevil: . And there could be some great rides that deal with the myths and stories from these places like An adventure into a Pyramid, or the Trojan War, or a visit to Mt. Olympus, etc. I think this idea would work and films like Hercules and Mulan would have homes and give good themes for kids' rides.
What does everyone think?
-Josh