Titles like "Toronto, London, Budapest meetups-June" could work for this.
I was just thinking about how generating a post like that could be automated, and thought: Why not just make a meetup announcement section, with a meetup announcement widget visible in the main section? "Meetup Date" should be an attribute of a meetup announcement, and the widget should show all future meet ups (ordered by meetup date/post date?) This would get meetup announcement out of the main post lists, but keep them visible on the main site.
For site redesign, go to the thread calling for redesign suggestions, linked in the OP. This is just an interim proposal.
The Less Wrong feed is getting crowded with meetups rather than substantive posts. Hopefully, this should be fixed in the redesign, but one way to work around it in the meanwhile would be to make top-level posts announcing several meetups at once.
Folk would post meetups under the 'NEW' category, and each week or even every several days one of the meetup organizers could edit her post to announce all the meetups since the last consolidated post. This would greatly reduce the cluster while still getting meetups in the main feed. On the other hand, it would reduce average warning time before meetups, and the additional activation energy might deter some meetups.
If you have thoughts on the workability of this scheme, or an adjustment to make it workable, please comment below.
[HT: Anna Salamon]