Actually, the admin staff had this idea in mind. They were originally going to use the green-roofed building in Barton Town with the music note to do this, though it would only support Gaia-based music. Unfortunately, they scrapped the idea due to other demands. *cough*GAMES*cough*
However, staff is still thinking about bringing that idea to life, just not right now.
You're kidding...right? Stream music. That's a bad idea. Example: Look at the post above you and then read what Desire said. How would they possibly cater to thousands of users who have completely different tastes in music?