I dunno, I would much rather retain the ability to download a new browser that promises improved privacy (i.e. by integrating with their own DNS service that includes pi-hole) than be limited to one of four well-known American OS vendors.

Alternatively, I see no reason why someone can't write a small application that runs a resolver on localhost, adjusts your hosts file accordingly, and forwards queries to any third party or distributed network of your choice. Wait a sec, I already have dnsmasq and/or systemd-resolved doing this on some of my machines. It can be done right now with no need to wait for the OS vendor to change things.