This one could have legs. Nearest X number of people gets around the 'this app is a desert' feeling - even if only 100 people are online globally, you've still got a full application!
I feel this results in some obvious paradoxes when considering how the room morphs over time.
One (contrived) paradox: 99 people in the world online in San Francisco and 1 online in London. One more person in San Francisco joins. Do the previous 99 SFers suddenly find they are talking to the new SFer and not the Londoner? Who does the Londoner see they are talking to?
Another (very contrived) paradox: 100 people are logged in who are all located on the edge of a perfect circle. One more person logs in who is located directly at the center of the circle. It's clear who is closest to each of 100 original people (presumably the person on the opposite side of the circle is 'swapped') resulting in each of the 100 original people now talking with the center person, but the center person can not be talking to all 100 people and there is no distance-based criteria for determining which of the 100 to not talk with.
These seem like contrived examples, but as soon as the total user count is greater than the 'nearest X' count they must be addressed. A solution would be fascinating, I don't see a clear one!
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.
