The project is tentatively called 'The Magic Kingdom', and weirdly enough 'Battlestar Galactica' creator Ronald D. Moore (I know, the remake, not the original -- but still, it's an entity unto itself, damn it) had a go at the project, having written a full script for the film. Then again, Disney execs are reportedly still seeking a screenwriter to continue work on the script; one that may need to focus more on a story that works in all these other characters. The vibe they're going for is one that's similar to the 'Night at the Museum' films.
That having been said, 'The Magic Kingdom' is not a top priority at Disney right now but it is something that is being seriously thought about. Instead, execs have other projects on the front-burners, like 'Tron: Legacy' in December, as well as film version of Disney rides like 'Jungle Cruise', 'Tomorrowland' and the previously mentioned 'Pirates 4' and 'Haunted Mansion' projects. Plus, if Disney is going to work in multiple characters -- like Mickey, Donald, Goofy, etc -- they're going to want to move slowly and carefully as to not put out a film that hurts these characters' images in any way.
Will it happen? Probably. When? We don't know yet. Could you see something like this working for Disney?
Variety's article also mentioned that Disney apparently has more weird and interesting projects based on theme park rides headed down the pipe, though who knows when or even if they'll happen. They mention that Guillermo del Toro is tapped to direct a Haunted Mansion movie, but as of now and that David Fincher is helming a new 20,000 Leagues Under the Sea adaptation. There are apparently also scripts based on the rides Jungle Cruise and Tomorrowland in various stages of development. Still, I kind of wish Ron Moore's Magical Kingdom was still on the table.