Adding new groups

I'm certain this has been discussed before, but seeing that
A: There's no search function and
B: Maybe people who joined since the last discussion would like to talk without necroing anything

Is there a cycle/timeline for adding new groups as interest seems to appear?
What's the plan for how to choose which new groups get added?

If not, could we (and the site's staff) discuss possibilities on good ways to do that?