Disney is better off using the Legoland model. Buy up a struggling park and remake it as the third park. I can think of SeaWorld in San Diego as the perfect park for such an endeavor, but it needs to buy the chain of 3 or 4 parks. Disney will instantly have 3 parks in Southern California, 5 parks in Orlando, and 1 park in Texas. It will have to transition out of owning marine animals eventually. Maybe too late anyways if SeaWorld goes private (as the current rumor).
The problem with opening more parks is Disney still haven't fully realized it's potential with its existing parks. Disneyland/DCA and Disney World's 4 parks are still not fully built out. Each park except for the main park has enough space for many more attractions and rides. They should invest billions more. Epcot, DHS, and Animal Kingdom should each add 10 more attractions. Disneyland Resort has so much open space for hotels and attractions, it's like what are they waiting for? Maybe wait for another city council that will screw them over or they sabotage their IP land by doing sequel spin-off or going WOKE with their IP properties. What happens will happen at Disney.