@gumnos yes, it would require the IANA to reserve .unix for UNIX sockets to avoid collisions.
The RFC specifies how a user can override a system-wide UNIX host by setting it in their own unix.hosts file (maybe at ~/.config/unix.hosts), which takes priority over /etc/unix.hosts.
Using "socket:" doesn't specify the protocol to use *inside* the socket. A single unix socket could serve multiple "hosts" via HTTP by using the Host: header. What problem does using the full path solve?