a cyclists with headphones is called a speed bump, really I ride & would never do that!!!
Look at motorcycle headsets & motorcycle radio designs/set-ups, that I think is where your market would be.
It could also be useful for online gaming, just add a mic for talking.
I am a AS-level student studying Product Design. I am undertaking a project this year on headphones, where I aim to design headphones that will make it possible for user to hear the music and also other surrounding noises. This could mean headphones that aren't exactly placed directly onto the ears but placed on your shoulders for example. The thought behind this was that people like cyclists need to hear surrounding traffic noise whilst cycling on the roads with headphones on. The final designs haven't been finalized, however I was just wondering what other headphone enthusiasts would think of this idea and whether they think it is a good idea. Your views on this issue are very much welcome.