That's what they need. Wasn't there some DJ game a while back, during the music game craze? I think they even had hardware turntables. I'm not sure how much freedom was in there, but imagine at least being able to spin, mix, and scratch from a number of different tracks and samples... all using your hands and fingertips (controller also an option, of course).
And yes, with Fantasia, I would LOVE if I could make the music louder and more intense, and make it more vicious and wild if I got very vigorous with my hands. Not shaking them around like I'm getting stung by bees, but controlled, firm movements. Like a conductor. And you could swipe in icons form the sides of the screen that could represent different notes, or a different genre of music to mix and blend in, or something. Complete freedom. Like a mix studio, but in the style of Fantasia. And you could of course share your mixed tracks, and maybe you could even customize and artistically draw in things on the background - like fireworks and fire - attach that to your music. That I would like.