Previous graph is for the MY1018z 24V motor with the OEM 9T sprocket.
Stage 3.
In order to operate pedals without using the motor the use of a freewheel sprocket on the motor is required.
The smallest compatible freewheel sprocket I've found is a 13T.
Of course, this will vary the motor applied speed noticeably.
MY1018z motor @24V w/13T sprocket
Sadly, this loses much of the low speed torque advantages of a multi-speed mid-drive, might be OK on a 20"er?
On the other hand...
In lowest gear as I am accelerating from a red light, I hit 10mph at my max pedal speed.
So I would be shifting right at maximum torque of motor and pedal assist, maybe ... not so bad.
Personally, I could be happy with a 9T sprocket with motor always engaged and pedal assist.
Optimally shifting at a more casual 60-70 pedal rpm.
A larger chainring from the motor can offset some of this loss.
With an intermediate jackshaft, most any gear ratio can be accomplished.
Stay tuned for more developments ...