What about automatically chatting with ANYONE nearby you that is using the app and "available" for chat? I think this will be a good idea. Imagine you in traffic, and launch the app to chat with the driver in the car side yours... The same could works when you go to party and don't try to find somebody "available" there.... This, for Facebook, should be easy, right?
Do you seriously think that wouldn't just turn into a chatroulette insta-dong service?
I think today one of most "popular" whatsapp feature is group message. Now imagine "localizated" group message formed automatically!
When you go to a Rock concert it will be possible to chat with everyone there, make new friends, chat privately and so on...
Actually it will be: chatroullete + whatsapp + tinder + Facebook Nearby :)
Maybe I should put this idea on IndieGoGo...
I'll wait for some feedbacks where first...them maybe I create an campaign there :)