I wanna be a keytar hero!

This is a concept I have for either the next project or the one after. The phenomenon of Guitar Hero has piqued my interest, and I wish to create a kind of music synthesis device. The basic idea is to have a sliding cluster of buttons attached to a light sensor that would change pitch/octave depending on the tonal value of the fretboard. To play a note I was also considering the idea of installing a range sensor that would alter the sound depending on how far your hand was from it, although I might also just make that a push button as well. Combined with some sort of visual representation of the musical notes, this instrument would be a visual and aural device that could compose compositions both on the screen and through the speakers.