Well said, Timmay. Many seem so concerned that the "theme" of Tomorrowland will be lost - especially after the expensive and extensive 1994 rehab project ("the future that never was"). I'm not sure what theme that was. Indy cars? Never really fit that theme if you ask me. Dreamflight? Heck, we've been flying since Orville and Wilbur Wright. Alien Encounter? An alien attack that could have occurred in any science fiction time line. The point is, as you correctly note, we don't know anything about Monsters Inc. attraction - if it indeed is the choice.
As to the Pixar/Monsters Inc. criticism... Face it, Disney has spent millions upon millions of dollars for this wonderful asset known as Pixar. In order to reap the most benefit from that investment, it is imperative that attractions (yes, multiple attractions) are created using these wildly popular movies as vehicles to promote that acquisition. Walt did the exact same thing with Peter Pan, Cinderella, Snow White, Davey Crockett and, yes, even the castles that are the focal point of each Magic Kingdom. Those characters provided the vehicles for attractions and marketing in their day and are clearly "classics." For this generation, characters like Buzz Lightyear, Mike, Sully and Elastigirl will assume those same roles and will likely be viewed as classics by future generations.