Brilliant idea and far better than what Google or Amazon offer.
With Google/Amazon I first need to upload my music collection to them, and depending on how much music I've got that's going to take some time. Once it's uploaded, I'm going to have to pay for storage of all those GB's they're keeping for me.
With Apple, any song I have that's also part of their catalog doesn't need to be uploaded - it'll play straight from the main copy on their servers instead. With Google/Amazon, you could literally have the same song stored hundreds of thousands of times over - one copy for each person in their own private "music locker". Not very efficient, IMO.
Without any deals signed with the labels, Google/Amazon aren't going to be able to make a single copy of a song and stream it to every user who has this song in their "music locker", so they can't get around this "storing one song numerous times" issue. So Google/Amazon will require far more server storage than Apple to provide could music.
And with Apple, I can still upload my own content if I wish. The big difference is that of my 30GB of music, probably 25GB will already be in Apple's servers and I'll only need to upload the remaining 5GB of my own stuff. Much easier to do, and I'm going to pay less for storing 5GB than 30GB.
So I get the best features of Google/Amazon (my own music locker & streaming to anywhere) without having to upload everything I've got or pay a larger storage fee.
Hate on Apple all you want, but they got this one right.