It's still a cool prototype, and there's still cool stuff you could add. For instance, if I were to use my phone as an extra keyboard for shortcuts, etc., I'd probably have it tethered via USB. USB device identification should be handled in software, so it stands to reason that your phone can pretend to be a USB HID device (similar to what is done in this[0] paper). Having a simple scripting layer would be interesting too. Trackpad wouldn't be bad either.

Another thing that could be cool is having your phone pretend to be a USB webcam.

[0]http://cs.gmu.edu/~astavrou/research/acsac10.pdf