While I think that filming the movie in B&W might be good for it, I don't think it would be a good idea as far as attracting an audience. While we, as devoted DS fans, would already appreciate it before we see the film, general audiences wouldn't get the atmosphere that black and white would add, and I'm sure it would be highly publicized that the film is black and white, especially in a world where everything has eye-catching special effects. That media coverage would certainly, IMO, kill the chance for bringing in new fans.