As noted above, "ever" is a long time. Humans have an innate inability to envision things beyond their own lifespan. Barring some nuclear holocaust or galactic collision, WDW will still be around a thousand years from now. Many thousands even. There is no reason to think that the first 50 years are, or will be "all there is". So yes, some day there will be expansion. But the upcoming transformation of DHS reveals that no fifth gate is contemplated in the next 20 or so years. Star Wars, Avatar, Pixar and Marvel provide lots of opportunity to branch out in a new direction for a fifth gate and they aren't biting. Maybe some day if Disney ponies up the billions necessary to buy back the Marvel rights, something might materialize. But until then, if George Lucas, James Cameron and John Lasseter are all pigeon holed into existing parks, it is going to take an entirely new generation of IP to muster up the foundation for a new park. "Villains" ain't gonna do it.