It could go under the "geekhack community" section at the end, perhaps. Right now, with the exception of the Chicago Keycon section, meet-ups seem to be organized in an impromptu fashion under the "off topic" section and elsewhere. Having a more prominent placement might encourage more meetups to occur! It would in any case help with visibility of ones already planned.
It also wouldn't necessarily have to be meet-up specific, but something like "geekhack local", etc., and could be used for things like meet-ups of local individuals who have boards and switches and want to trade test drives, etc. Could be a general "Boston thread," "Chicago thread," etc., for one-off meetups like this, and specific threads for particular organized large-group meetups such as, say, "NYC Meetup 20 Oct 2013", etc.
The thought occurred to me because I was thinking of trying to get together a meetup here in Boston (and am pretty sure I can provide an excellent venue right on the Charles in Cambridge, overlooking the city skyline), and I didn't know where to go about starting a relevant thread.