According to iPodNN, a patent application that has been submitted to the US PTO suggest that the control wheels for future iPods may have touch based illumination. The article also states that the same function could be applied to touchpads on MacBooks.
While I think this would be cool to see, I’d like to see the control (specifically on an iPod) pulse (multiple colors?) to the music playing. Pressure based LCD or OLEDs? Hmm…