A bit strange to me how Josh beings with heralding the browsers working together and then every mentioned feature is Chrome only. They're nice previews for a potential future I suppose!
It feels like Interop was created to curb Chrome's bulldozing various processes with their own internal APIs and development, and to show that there's more to the web than yet another shitty Javascript API. So a lot of Interop is decidedly everything else. See e.g. Interop 2022: https://hacks.mozilla.org/2022/03/interop-2022/
Of course Chrome bulldozed this effort as well
[1] https://open-ui.org/ Started by Microsoft, of all people. Now almost completely taken over by Chrome of course.