like running an ol TH400 slush box in the RC car. I think i have seen 3 speed trannies for 1/8 off road nitro.
Those shift on simple physics and not electronically.
You would have to keep RPM tabs on the motor, and then program whatever it is to shift at certain points (if doing an auto instead of semi-auto) to the next gear. I'd be curious on the amount of force needed to do this from a servo/pneumatic valve.