Ritz-Carlton in Orlando has seen quite a bit of success, as have the rest of the 4 diamond properties. The Ritz is the closest you're getting to 5 Diamond though. I think 4 Seasons might change that, but that isn't even a guarantee.
Joke if you want but I think there is a real market for 5 Diamond in Orlando. It would obviously come with upscale restaurants if it happened. These people are already staying in Orlando, that's why there are so many 4 Diamond resorts in Orange County. The people staying at the Ritz, Grand Floridian, and J.W. Marriott are close to paying 5 Diamond prices as is, there money is ready, they'd more than likely pay the little bit more to stay.