sorry, forgot about ftp:// and ws://. i think your comment is a better approach than the original RFC. the hosts file approach is overwrought, and trouble waiting to happen.
First, it is easier and shorter to type and remember, as the path to the socket can be long. Second, multiple users may run a given service in a socket located at different paths. And third, using a host name can be used to create virtual hosts, so you can serve different responses to foo.unix and bar.unix while both point to the same server UNIX socket.
If you see a problem with using a host file, could to provide an example of how it could go wrong?