My Guess
When you select a preset (5 pc band for instance) holographic 3D images of the players and instruments will be projected on stage, then when you play your board the images will play the instruments, if you have a Saxophone and a Trumpet player then when you play the Sax the Saxophonist image will play, and when you select Trumpet the Saxophonist will refrain from playing while the image of the Trumpet player will start plying the Trumpet.
But then who knows what the future will bring

Bill

not trying to steal the topic!...
but, there was a movie i saw once, can not remember the title, a SF movie i think, where they had some sort of instrument to play by the hand, as high the hand moved, as high the pitch was... and everything was only lights and beems...
the real big disadvantage... the instrument must've been monophonic!

As long as the music wasn't monochromatic...!

Theremin
http://en.wikipedia.org/wiki/Theremin

I have some links to Theremin websites at http://www.synthzone.com/others.htm