Yes you could use the leap for actions like turning a knob, but you would have to write the app or front end software to utilize it. They are fairly cheap, and fun to play with. It's just that there are still easier ways to do stuff like using a Griffin Powermate for volume control, and a touchscreen.
My car is too bouncy while driving for minority report type controls though, unless I figured out a way to make my whole windshield into a heads up screen. I do have a specially coated HUD windshield, which can reflect my phone, the cars HUD, and a flat screen off the windshield if I get to that point in the hobby someday.