Creation of playlists online would be very hard to do. First, we would need to know the songs on both the desktop/client at all times. The amount of BW required for this would be immense and very costly.
Using the proximity service, we could instead just sync folders. The user could then create the playlists locally on the system and then when the sync happens, the playlists get downloaded to the client.
What are your ideas on this?