Those are both reasons that .local should be static DNS on the _network_ like localhost is a standard name for the loopback address(es). There's no reason .mdn

Those are both reasons that .local should be static DNS on the _network_ like localhost is a standard name for the loopback address(es). There's no reason .mdns or .mdns.arpa couldn't have just been added to the default domains search list (the list of suffixes tried for non FQDN searches); which given it ISN'T a nice human obvious word to append wouldn't have conflicted with anyone who'd already had a .local at the time, and anyone else in the future who thinks an obvious phrase like .local would not be in use by some other resolver system.