I know that Steam Music is already in the works. It makes sense that Steam expand into music, books, even videos as games and their tie ins become more prevalent. However, there are a few things I'd really like included as it pertains to music:
1. A subscription option similar to Spotify w/more game music soundtracks available. 2. A social sharing option so we can share playlists for games. Hats/Cards/Rewards should apply to encourage the sharing of awesome playlists. IE-Add a heavy metal soundtrack to TF2, etc. 3. "Steam Music Supported" so to speak for games. What do I mean? Have hooks so that developers can hand over some power to the players so that players can customize playlists depending on what's happening in game. This would allow for fun and interesting playlists that players could send around and even allow developers to create in game playlists of music that they could never license themselves in a cost effective manner. This could also allow the music to be automatically muted for dialogue, cinematics, whatever. 4. User created music. We allow user created mods/skins/etc. Why not allow music to be uploaded and shared? This would also allow some users to earn some money, just like they do creating maps. (Let it be known I am in no way saying this for myself. I have no interest in creating music, but there are so many amazing game music composers/artists that I'd love to support. Malukah anyone?) 5. Artist pages. Like an artist who created some awesome DOTA2 music? Follow what projects she's working on. Be able to donate to that artist. 6. Allow Steam Music on mobile as well as Steam Boxes. 7. "Steam Music Supported" multiplayer games allow currently played playlists to be shared with other players within the same game. Perhaps even "synced" so we can all sing along together in drunken stupidity. 8. Top Playlists/Songs: Order by game, region, friends, etc. Fun way to explore music.
Anyhow, those are just a few ideas. I just hope that Steam Music is more than just an in game music player and really leverages the steam community and the cooperative/competitive nature of games. What do other people think?