Disney has filed a trademark for "Castle of Illusion, according to Siliconera. Back in the 16-bit era SEGA licensed Mickey Mouse from Disney for use in side-scrolling platformer Castle of Illusion, but it seems Disney wants to do something with the title now.
It's not clear if the publisher is simply looking to release the classic game as a downloadable title or if bigger plans are in place. A sequel to last year's Wii exclusive Epic Mickey has been rumoured, so perhaps the trademark has something to do with that follow-up title.