> APIs like these don’t exist for the sake of regular unprivileged web-apps. They exist for the sake of browser extensions (or browser “apps”, or apps within a browser-projector like Electron), specifically in order to be used to add driver-like or service-like capabilities to devices like Chromebooks where the browser is the OS.

That's not really true, though: they're part of the Chrome team's belief in not limiting the capabilities of the web as a platform for app development (on the basis of "if you lack one feature the app needs, the entire app ends up native"). This is a large part of Project Fugu: https://developers.google.com/web/updates/capabilities