I’d expect implicit localhost to behave just like any other host when it comes to loading variables from host_vars.
But it doesn’t load vars from host_vars/localhost.yml nor host_vars/localhost/somefile.yml
Of course, it behaves as expected when it comes to group_vars (it loads group_vars/* but no other group).
I’m coming from https://github.com/ansible/ansible/issues/9750 where I’ve added a link to a commit from @sivel that solves the issue.
https://github.com/sivel/ansible/compare/ansible:devel...sivel:implicit-localhost-hostvars