I'm sure it works fine, but .mil is a real TLD and someone (like the new Space Force or whatever they call themselves) could register it and use it publicly tom

I'm sure it works fine, but .mil is a real TLD and someone (like the new Space Force or whatever they call themselves) could register it and use it publicly tomorrow. The ".home.arpa" domain is explicitly set aside for 'home' non-public networks in https://datatracker.ietf.org/doc/html/rfc8375 https://datatracker.ietf.org/doc/html/rfc8375.