I do not really understand what you mean by this. Can you elaborate or clarify what you mean?

I mean since it's linux phone with (hopefully) open architecture, it should be possible to create an external usb device that exposes any functionality.

Like, to keep core functionality simple and open it for extensions ("extra battery", "knobs and switches", "ethernet" etc)

But if it does not really cut the power to hardware components, how will you trust that it turns your mic off?

Yes, this is what I'm getting at. I want to KNOW that the function is off, and that nothing can turn it back on except a physical action by me.

There are many other use cases, physical control are not used only for cutting power of components.

I don't think that's what anyone means by "physical controls" and if they do, then they don't know what they are talking about.

"Physical controls" are those that you can physically sense. My point was everyone needs different things, so it's possible to keep core functionality simple and let users add what they need, via extensions. Like dongle hell but better.