I don't think that quite fits into the security model of many of the purposes for which people use localhost, as they often want to avoid all external dependencies (including Internet access!) and all external trust.
If they do use your domain name then they have to trust that nobody has subsequently seized the name in court, nobody has hacked or DDOSed your nameservers, there's not an interruption of network connectivity between them and your servers, and that the ISPs forwarding the DNS queries didn't substitute a different response for the one you intended to return (since currently your leaf records aren't DNSSEC-signed).
If they do use your domain name then they have to trust that nobody has subsequently seized the name in court, nobody has hacked or DDOSed your nameservers, there's not an interruption of network connectivity between them and your servers, and that the ISPs forwarding the DNS queries didn't substitute a different response for the one you intended to return (since currently your leaf records aren't DNSSEC-signed).