USB-C permits analog audio passthrough so you could literally use a passive headphone adapter for the antenna but it's a feature rarely supported anywhere.

Not anymore, that mode has been deprecated since USB C 2.3 (released last year). Almost nobody actually supported it in reality though.

I'd expect so. It's basically like an analog TV capture card for your computer— but the use cases are even more limited as it's hard to imagine your phone being the platform on which you'd want to record stuff off the air.

I guess it could make sense if the phone is driving your wireless earbuds or you want to change stations using Siri, but yeah other than that, I dunno.

Seems like the market would be people without unlimited internet. Audio takes up a fair bit of bandwidth over time so being able to listen to your personal music or the radio in your earbuds might be considered useful.

It’s not exactly what you mean, but a nano RTLSDR, a usb C adapter, and any SDR app can do what you’re outlining and far more.