(changed the subject to make clear that this is NOT about Alt-Svc anymore)
I assume this is limited to onions for sites that do not aim for server side location anonymity.
FYI: the proposal is now the first Tor Browser proposal: https://gitweb.torproject.org/tor-browser-spec.git/tree/proposals/100-onion-...
in the light of the fact that this proposal has been started before Tor Browser 8 with Alt-Svc support for .onions was a thing (and CF jumping on it [0]) I'm wondering how you think about it compared to what benefits Alt-Svc provides over what Onion-Location provides?
Are you unsatisfied with what RFC 7838 - HTTP Alternative Services provides or is "onion address is displayed in URL bar" one of your goals/requirements of this proposal?
Although Alt-Svc does not work reliably _yet_ and the UI part is missing [3] I find it addresses some rather important issues that 'Onion-Location' does not:
- users get the transport security benefits of .onions without Tor Browser displaying hard/impossible to remember/recognize randomly looking strings.
Long randomly looking strings in the domain part of the URL that would probably confuse many users and make it harder to answer the question "Am I still on the page I want to be?" (I consider it a major UX improvement that you can display the non .onion domain name while the traffic actually goes to the .onion)
- users will use onions transparently without asking them questions they probably don't understand or don't want to be bothered with everytime they visit a website [1] I believe asking fewer questions, safe defaults and configuration options for advanced users are some reasonable goals.
- it solves the ".onions can't get DV certs (yet)" issue
[0] https://blog.cloudflare.com/cloudflare-onion-service/ [1] https://trac.torproject.org/projects/tor/attachment/ticket/21952/21952.png [2] https://trac.torproject.org/projects/tor/ticket/27590 [3] https://trac.torproject.org/projects/tor/ticket/27590#comment:2