Hmm..

How about having an app that broadcasts a hash of your interest\keywords and alerts you when you come close someone with similar interests? This way, only those with exact interests\keywords will find each other. Then once application connects, you can have some sort of asset sharing areas (medias, web page, etc) for you to browse and exchange content.

Of course it should be made with plugins, this way any apps can take advantage of this system.
A common example for the plugin: a poker game can use this to find opponents around you

Yeah, this could be used in creepy ways too But don't you think it would be an interesting ways to discover mobile and dynamic contents around you?