@blog I suggested something similar for #libravatar some years ago https://gist.github.com/aslakr/6a7306bf74080eea4498c19fb418073a when services can't use the DNS records.
I also think that services like this should have a way to indicate the size of the avatar, similar for libravatar/gravatar.
Gist".well-known/avatars" as an alternative/addition to DNS SRV for federated libravatars?".well-known/avatars" as an alternative/addition to DNS SRV for federated libravatars? - well-known-avatars.md