As far as new IP in the parks, I would expect something X-Men related and probably not until after adding X-Men to a new MCU film.
As far as Disney adding a 5th park, I believe the issue there would be that the city of Orlando would not support it.
Don't Disney govern their own land there in Orlando? therefor surely the city has no say? i read about this a few years ago in that Disney can pretty much do what they want within reason on their land.