Yeah, I have some ideas about including different data sources. You have to start somewhere, though, and Meetup.com has a nice real-life aspect to it. My best guess would be that Github and HN would add most interesting data from a technology / community popularity and natural language perspective respectively.

Question is: how do you connect a Github repo or a HN post to a specific community? Content based? User based? Topic based? The community detection in the real life Meetup.com network is at the very basis of this and for good reasons, so you'd have to find a way to tie other data to that idea.