Indeed, or: I like this person A, lets see what kind of music he or she likes. Or if you got a hit on a certain band or genre, you get alarm and look into. Or 'you see' (your device, who read their metadata, actually) a person plays a music instrument, and you detect, read profile, and decide to chat because its missing link in your band.

Thing is, there is issue of privacy. You don't want people to know your whole history after they know you for 5 minutes. Some things are meant to be shared later, or never, or only with certain people. So there will be need for ACLs.