Hayao Miyazaki's Little Nemo Test Film
So it turns out back in 1992, Hayao Miyazaki was working on an animated film with Isao Takahata (Grave of the Fireflies) that never really got off the ground. Based on the American comic "Little Nemo," the film was to be a joint project by Japanese & American animators. All that became of this would-be classic is the test film that was used to pitch the film, which can be viewed above.
In edition to Miyazaki & Takahata, big-time American names such as George Lucas, Chuck Jones, Gary Kurtz, Ray Bradbury, Chris Columbus, Moebius, John Canemaker, Leo Salkin, Paul Julian, Ken Anderson, Frank Thomas, & Brad Bird were all attached to this project at one point or another as well. But as said, the movie was never able to get very far. What could have been, what could have been.
Source: http://www.cartoonbrew.com/anime/little-nemo-test-film