I think you might be right on this. If I signed up to a service like this and there was no one in my area, but the app suggested that I might like to chat to these 50 odd people online in London or San Francisco, I might well stick around.

I don't know how you would work it for an app that is supposed to be all about local though. If I sign up, and get connected to, say, some guy called Brian in New York and the conversation is great, but then the app grows really quickly and all of a sudden the app decides Brian isn't close enough for me to talk to anymore, it might leave a sour taste.

There are definitely exciting UX possibilities with this though. I need to think on this a bit further.