I think it's an interesting problem space, but user initialized meetings might be a better way to go. My availability is not going to be accurate in any app that I wasn't constantly fiddling with, and I wouldn't be constantly fiddling with it.

That said, a lightweight mobile app that allowed you to set up meetings based on interests, suggested meeting places/times when you did so, allowed you to set a threshold of interested users, so the initializer isn't sitting in a starbucks by themselves, and notified you when you were near such a meeting might work for me.