Now that the Walt Disney Attraction with film has been cancelled (or put on hold), I'd like to throw in my 2 cents. This was an idea I originally had for the MK at WDW (to replace the Walt Disney Story), and it could work in the "new" DCA.
The problem with many of the tribute attractions to Walt Disney is that they are theatre presentations which lose the interest of the general public once they've seen them. Why not create a Walt Disney tribute using an omnimover or even a Model-T type car (think Mr. Toad) and travel though Walt's life. You could travel through his boyhood home, down the Main Street of Marceline MO, then showcase his early achievements, followed by a trip down train tracks (from NY to LA) with the story of the developement of Mickey Mouse unfolding around you. The ride could take you through the opening of Snow White to the opening of DL. It could continue right up to the day that he passed away. Using all types of media in the attraction (from set pieces to film to models to animatronics), this type of attraction would appeal to everyone (and accommodate every member of the family). Kids would love the ride through appeal, while "older" kids would love the history. The Disney "Geeks" (me included) would ride the thing over and over. Incorporate an optional museum/exhibit type area after the ride and you'd have a great balance of what Disney NEEDS, an attraction that reminds and/or educates people of who the man (men-if you include Roy in the picture) who created this entertainment company, presented in a way that draws the masses in and doesn't put them to sleep.