Browsers are the only ones actually willing to allow any change. If we wait for OSs to change nothing will ever happen. If it works well in browsers first then the OS will pick it up.
Browsers should respect the OS instead of trying to circumvent it.
Lastly, DNS is properly decentralized out of the box. I don't get that some people who argue for a decentralized internet also argue for DoH.
DNS is also not decentralized. It's centralised on ICANN and whatever company owns your TLD which is why this thread is here.