I'm not talking about the browser doing the name resolution. I'm talking about the opaque binary running inside the browser doing name resolution (either by way of DoH with a pinned certificate, or a custom name resolution protocol running over TLS). You won't get a say in what that opaque binary does (w/o modifying it).

Is anybody doing this now? I doubt it. Will somebody do it? Yeah. Definitely.

When the "browser" is an embedded device (like Google Chromecast devices hard-coded to use 8.8.8.8 for DNS) you'll have no configurability there either.