We did try setting something like this up on Physics.
It's a question on meta, where people who want to be pingable, each give a single answer, in which they state the specialities on which they want to be pinged.
And then, in theory, if anyone wants to ping you about a question, they can just leave a comment on that meta answer, with a link pointing to the question. Once you've answered the question, the comment can then be deleted.
Nice theory, huh?
Only thing is, it's almost never been used.
It's also worth quoting what David Z said in a related meta.physics question:
Sure, having a meta question where people can "register" their interest in being pinged sounds fine - at least, there's no rule against it. It wouldn't hurt to try it and see if it helps at all. It wouldn't be featured forever, but we could probably put faq on it if you word it the right way (e.g. "How can I ask someone specific to answer a question?").
However, I would encourage anyone who would be interested in participating in such a system to also do the following three things:
- Include your areas of expertise (those in which you would like to be "pinged" if a pinging system were available) in your profile text blurb. If you have enough reputation to have a "user card" (the thing that pops up when the mouse hovers over your gravatar), then make sure your areas of expertise show up there.
- Also include those areas in your chat profile.
- Stay logged into our chat room as much as possible, and check it periodically to see if you've been "requested." Let's make that the central place to recruit people to help with specific questions.
I think this is the best way to use the existing system to accomplish the goal here - and at worst, it's not going to interfere with the meta post.
(I've amended the links to point to academia rather than physics)