That's what I was thinking about - inner-ear bluetooth stereo headset that does the basics like notification pings, but perhaps also act as a 6th sense, things like navigation cues so you can use your navigation app on your bicycle without blocking your hearing or looking at your phone.
Also think self-tours. People could setup tours around places like Rome and vote them up. You load it up, then walk around the city getting tips on the hot spots and history. I believe there is a lot of potential for this sort of contextual audio cuing.
