According to Jeff's answer, @replies to post editors are implemented:
So you can now @reply to editors of a post even if they haven't commented.
Yet, I just tried to address the editor of a question in a comment and couldn't. No auto-completion of the name. I typed it in anyway, but it doesn't seem to have reached the editor. I tried it at another post where the same user commented and the @reply worked as expected there (auto-completion and everything).
Happened with this question: SQL query issue (with screenshot)
I haven't changed anything further so I wouldn't contaminate the crime scene.
I ran some tests with OMG_Ponies, and he did get the messages. So, it's only the auto-complete that doesn't work as expected. And the
_ in his name helped to fool me at first.