I think headphones are the biggest candidate for waterproofing. Albeit we may not have that much of a demand for headphones that you can wear underwater, and listen to music at the same time, since we need more actual devices that can withstand being under water for extended amounts of time. Maybe if we can get them powered by WiFi, instead of just regular Bluetooth, we might be able to get people willing to leave their phone at the side of the pool (lake? beach?) so we can have much greater distances between transmitter and receiver.