I actually tend to agree with the side that says that Disney Theme Parks are ok without the thrill rides. However, I do think that Disney could afford a thrill park (or two) that are more half-day parks
I would suggest first opening Disney's Coney Island as the fourth "area" of DTD past Cirque. This would look like an actual island, with a small "city area" around it and, eventually, Disney's Metropolitan resort, complete with rooftop pool. As for the park, have a faithful copy of the Cyclone, traditional classic Coney Island Rides, two dark rides (a Princess tunnel of love, and a Spook House that turns into a Monsters, Inc. ride somewhat in the vein of the new one for DCA - although I swear I had the idea before they brought it up!

), etc. It would be top-designed versions, however, with white lights everywhere and a small staff that changes the lights daily. Also have recreation of the Coney Island parachute tower at the tip of the island (in the lake) that is a more thrilling drop version of the classic parachute ride.
Second, I would put a thrill park attached to the Wide World of Sports. Named something along the lines of XZone (although I don't like that name), this will serve as a showground for new, intense ride technology. Divided into major zones depending on effect, areas would include G-Force Zone, Fall Zone, Inversion Zone, Speed Zone, etc. Each would have one or two major attractions. While the rides will be more Six-Flags in nature, they park will be very nicely landscaped with interactive displays everywhere (that are safe). It also, ala Epcot, will have an area in each Zone that displays what those forces do to your body. Each attraction will also have a large "Chicken Stands" area where people can simply sit and watch. The largest area will be the Test Zone. Developed as a partnership between major ride development companies, they will be able to erect finished concept designs (like Huss's Frisbees, Top Spins, the Arrow pipeline coaster, etc.). WDI will design the area itself, and the companies will provide the rides (independently or with financial help from Disney, depending on Disney's position on it). Note this will not be a major Coaster Park but rather a thrill seekers park wtih small foot-print rides. That way, technology can be exchanged quickly, and it will not operate as a major detraction from the other parks.