A lot of times I find myself doing some work very late at night (eg, when most users are not) - so if I ask a question about a particular topic, it might only hear crickets unless I bump it the next day (which sucks).
What I'm proposing is that, after a certain reputation (say, 1000), you can see approximately how many people are online that are interested in your "Interesting Tags" list. So, if I have a question about something obscure, I wouldn't have to just shoot it into the dark; I could ask it more strategically so it's more likely to get exposure, get people talking, and get everyone's questions answered.
The reputation requirement would be mostly to avoid discouraging new or unestablished users from posting; users who frequent the site/have a high rep are certainly going to ask the question later - others may just not come back.
Any thoughts/amendments are welcome.