Exactly. All these ideas are nice but you guys are not thinking in terms of scale. Applying automatic transmission or even bike parts to something as tiny as a turbo is not very practical.
A sprag clutch for example:
Needs a good deal of running surface area at the rollers to transfer the torque from one shaft to another… IE its needs to be of a suffucient diameter. Try applying that to a 3/8" diameter turbo shaft (without a significant mass increase at the shaft)
Second: To start and spool an impeller assembly from a standstill or slow speed to boost speeds will take a decent amount of torque. …hence the crazy planetary gear sets in Centrifugal superchargers.
Now the smaller the diameter shaft(or gear) you are working on, the more torque is required to get it to the same speed. Trying to apply that to a 3/8 diameter shaft will be tough if not practical unless you find more surface area to transfer the torque or effective shaft diameter to reduce the torque required to accelerate the impeller assembly mass.