And those switches can go next to the ones for power to the camera, microphone, wifi, bluetooth, speakers, and anything else that I might want to be electrically disable-able, right?

Physical switches for the USB ports sound like they'd be as confusing for most people as the physical wifi switch was, when that was common. I think that means that if some manufacturer decides to introduce them, they won't be around long.

It's not nothing to hide, it's realistic threat model. But if these things become more popular and in more and more devices they'll just hoover up all the data they can get like already happens with web software. The average user probably should not have to learn what an extension is and figure out which adblocker to install, but this is the inelegant world we live in, and anyway I'm still on the fence for whether I really want to expect more from the average user or not.

Facebook will mass deploy these to serve targeted advertising based on conversations it hears.

This argument is similar to saying you don't care about someone else's freedom of speech because you have nothing to say.