Cartoon Brew has this to say:
It was an American/Japanese joint project, with no less than Hayao Miyazaki and Isao Takahata involved in the pre-production stage (1982-83).
George Lucas, Chuck Jones, Gary Kurtz, Ray Bradbury, Chris Columbus, Moebius, John Canemaker, Leo Salkin, Paul Julian, Ken Anderson and Frank Thomas were attached to this film at one time or another.
If all of that is true, this film could have been legendary. I can remember when I was in school one of my teachers, Corny Cole brought in a drawing he did when he was asked to work on preproduction for the movie. I'm not sure how long he was on it I only saw the one drawing. It was on a huge piece of paper that took up an entire wall. It was a drawing of the dream city. I was a big fan of comic books and comic strips as a kid. I ran across a lot of Nemo Comic at my local library so I was fairly familiar with the characters and the look of the comic. This drawing looked a lot like the comic, except that it was all drawn in ballpoint pen (Corny's preferred method of drawing, he even animated with the damn thing). The drawing was very inspiring, I wish I could see it again.
Here's an example of what Corny's ballpoint drawings are like: