The Honda semi-auto clutch I had mentioned in post #12 is more than just a typical centrifugal clutch. I hate most YouTube videos but the one I link here is good and goes into great detail about this mechanical clutch's complexity.It was a centrifugal mechanism, so whilst sitting at idle the clutch was disengaged and you just shifted the bikes into 1st gear. Then as you opened the throttle and the rpm increased, the clutch would smoothly grab with increasing force and you'd take off. Shifting required only backing off the throttle, making the shift, and re-applying the throttle. Sounds pretty much the same as what is described here, no?
For all I know, centrifugal clutches aren't amenable to the much higher output of today's engines vs. the 50 - 80cc bikes of the '70s. However, patentability seems like a probable factor here to me, too.