If your filter is based on the irc, and the number of people there is declining, basically it means that only the most hard-core users are remaining. And usually that means that they know how to use it.
Sure, if you're hiring people to be skilled IRC users.
But, I think what you're trying to hire are skilled software developers. It's apparently been left as an exercise for the reader to demonstrate any correlation between these two skills.
@munificent as the title of the post states IRC is a filter.. filter used after candidate is selected from a pool of people that have necessary skills, other than using IRC.. The author simply talks about selecting from this pool people that can use simple tools like IRC.
But, I think what you're trying to hire are skilled software developers. It's apparently been left as an exercise for the reader to demonstrate any correlation between these two skills.