I've never tried Google Glasses so I don't know if you can listen to music through them. But if you CAN, I would like Google Play Music to add a feature that would allow two people, both wearing GG, to see the titles of the songs each other are hearing, and then tune into that same song. If the audio fidelity of GG isn't good enough for music. Maybe Google Play could still be adapted to show what you might be listening to through your earbuds.
Out on the bike path today, I see so many people in their own private worlds listening to earbuds. Wouldn't it be cool if they could voluntarily make public what they're listening to, so anyone walking by with Google Glasses on could see the song title and hear the same thing they hear?