Multiple times, I see a question and feel "oh,
<xyz> would be able to post a brilliant answer to this one". Quite a few nice questions get pushed down; out of the notice of the specialists. Sometimes I may want
<xyz>s advice on a particular answer that I've seen. Aside from that, there are numerous other reasons where you may want to contact a specific user. For this, I proposed a feature at MSO, but it probably won't go through.
So what I propose is this: A meta question, on which a user can post their username and specialties as a separate answer. A user need not be a specialist in anything(eg, me) to post. Maybe the question can be tagged featured so that everyone gets a look-see at it.
The point of such a post will be to allow anyone to ping that user with P.SE related comments. It should be entirely opt-in, nobody's forcing anyone :).
Of course, there are spam issues and other stuff, so I want to see some of your thoughts on this.