Describe a version of your ideal user interface. I'm looking for visionary thinking here. Cost is no object (you can pretend you're Bill Gates, and you suddenly got a mad burst of creative enthusiasm about how to spend your billions). Post the answer to your web page.

No science fiction (ie: things that are physically impossible as far as we know). That rules out, for example, time travel or Harry Potter's Marauder Map (as wonderful an idea as that is for a user interface).

You can, however, explore things on the order of a pond of water where rainbows of color cascade out from your feet wherever you step, and if there are two people, the colors flow between them. Or maybe a new kind of interface for a car, or for a musical instrument, or a pen-based drawing program, or organizing your music collection, or lighting control for your office.

Inspirational images and explanatory diagrams would be very helpful. Your response should be a complete cohesive thought, not just a few evocative phrases (reading it, I should have a clear idea of what/how I would implement). No shorter than a few paragraphs, and no longer than a few pages.

I'm looking here for clear thinking, for identifying a problem and coming up with a creative solution for it. Fun and wacky is ok (eg: the musical umbrella whose playing is controlled through bluetooth by your footsteps).