+1Great suggestion! This could actually add quite a bit of expressivity to the P6. Just the possibility of controlling sync sounds directly via the wheel would be worth the effort. And as blewis has suggested in
this other thread, it would also allow for smooth (non-quantized) filter sweeps which otherwise aren't really possible on the P6.
As for the best way of implementing this though, it might not be as easy as just changing the behavior of a specific LFO waveform to output a constant voltage when the frequency knob is turned all the way to the left. That's because it would theoretically change any pre-existing sounds which use the minimum LFO speed.
So here's an alternative suggestion: On the P6, the LFO waveform is selected via an encoder and the current selection is signaled by an LED. Why not add another state after "Random", so when you turn the encoder another notch, no LED is lit, signaling "no waveform selected" and resulting in a constant DC voltage. To me that would seem quite logical and intuitive.