The first numbers for Apple Music are in and it’s an interesting amount. From Marco Cava at USA Today:
So the estimates of 10 million floating around last week were in the right neighborhood. Of course, 11 million users who aren’t actually handing over any money doesn’t really mean much at this point—now Apple has to retain those users after the remaining two months of the free trial are up.
I have your answer: make it worth their money. It’s easy to get eleven million people to sign up for something they can get for free with you but have to pay for, elsewhere. The key will be if the level of frustration coming from some has more or less weight than the idea of being able to use a first party app that ties in with your regular iTunes library.