I understand the issues, I wonder how the ns7 functions and if it would work with traktor instead of it's native software. I'm guessing we're going to need a pretty complex controller for this thing in order to use the scratch mode, I think you could make the motor belt driven so that the belt simply slips when you scratch, that'll save the strain on the motor. Hmmm to the drawing board we go, the scratch mode way seems to be the only option, we just need a good speed control circuit.
Perhaps if this fails, I can probably easily incorporate a touch sensitive platter to improve the thing, because if I build this thing I want it to be more effective at scratching than my omni board..