> The synergy drive needs a multi billion dollar semiconductor industry.

Your machine shop needs a multi billion dollar metallurgy industry as well. The difference is mostly the age of the industries, metal working has been around for much longer and the knowledge is nolonger confined to a small group.

This isn't about knowledge but ability. There are guides to build a lathe from scratch in your back yard using scrap metal. You can't do that with semi conductors.

Late to the reply, but someone can absolutely build an functional and usable eCVT with 50 era tech. And they could use manifold vacuum as a speed controller, like they do with old school automatics. People underestimate just how simple and clever HSD really is.

Or you could make it a "manual" eCVT where the speed control is managed by the driver using something like a potentiometer. This is how the linked CVT works in bike its applications (though, I'm sure it uses a controller built by the billion dollar semiconductor industry instead).