@dillo without a proper RFC/registration of a .unix TLD, this can cause possible problems. The footnote at that URL mentions that it doesn't exist, but that doesn't prevent it from appearing in the future. So if it were to move forward, I would want to see it officially RFC-spec'ed similar to .invalid or .local or .internal
The /etc/hosts (or unix.hosts) hack feels a bit…unfortunate. It prevents non-admin users (who can't edit /etc/hosts) from adding endpoints.
I'd much rather see it done via the protocol, maybe something like
socket:///path/to/socket:/path/to/resource