I have a pair of Shure SE535 earphones and they are fantastic. Perhaps the ergonomics could be improved, but I cannot imagine how the audio quality could be better.
I don't think the point is audio quality. Hearing aids do more than just have good audio quality; they serve multiple purposes, like connecting to phones or TVs. Presumably, one could build vastly better headphones by making them easily connect to whatever device you want, wirelessly.
For example, many gyms have TVs playing, and have a small FM radio station so you can tune into the audio with your MP3 player. Perhaps wireless headphones could support this seamlessly. Or your headphones could pick up an audio track played at a national park or tourist attraction, giving an audio tour.
We can do all these things currently, but they require hacks. Perhaps headphones could support them natively instead.
