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).