Radically changing the music experience
Looking back forever, music used to be about sharing. Around the campfire, at the village fair, with family and friends around the piano. Having that vibe in common is really one of the magical experiences music offers, and as a species we are extremely sensitive and receptive to music. It's engrained in us.
Recently though, music has become a form of shutting ourselves off from the outside. Everyone uses headphones. You are in your own little bubble. This changes the music experience radically.
Apple already has the framework: AirPlay. That and an ad hoc network:
-its easy: when one of your friends is nearby, just tap Airplay in the Music app and the friends name and boom he's hearing what you are.
I think this is a tiny thing that could really make our lives better, or at the very least, music much more enjoyable.