What's being hinted at here strikes me as rather pointless, too.
If Apple maintained databases of who owns what from one humongous library, then streaming it from a centralised repository would make sense *everybody would be listening to the same copy of the same song, and it would save an enormous degree of duplication.
If, however, they decided to continue along the route we're currently going along, in which each individual/household has their own library of music they like, tagged how they like and encoded how they like, then it makes far, far more sense for us to store these libraries locally. The network distance between the user and the stored file (which would anyway be unique to each user) would be a lot smaller, which is a more efficient use of data transfer (i.e. your music is streamed upstairs from your NAS to your computer, requiring a couple 'hops' and only operating in one subnet).