The really, actually simple solution is to change the terms for subscriptions and be done with it.
Realistically, Apple's not competing on price. I could've signed up for Rdio or Spotify ages ago and I know enough to do it online and save myself the 'convenience' cost of doing it in the application. Apple has already got the power of defaults working for it, really strong industry ties, and the fact that it doesn't bleed money hand over fist by having a free tier that can't pay for itself. Spotify loses money because so few of its users convert to paid subscriptions, but still makes the majority of its income off of those few (20%, I think?) subscribers.
I'm paying for Apple music (or I will be, when the 3 month trial is up) because it's integrated with the applications that I already use to listen to music, and my library is available to me without any extra effort on my part. It's too good to pass up, assuming I'm going to pay for a service at all.
Spotify (and everyone else) will NEVER make good advertising revenue because the people that the advertisers want to reach most—the people with money that are willing to spend it—are the people that have selectively removed themselves from the pool of people being advertised too. All they're left with is people that are either unable to pay, or don't think they should have to pay. It's a poor value proposition.
Apple doesn't need to bleed money off of Spotify anymore, and it's silly to keep doing it. The possibility of a lawsuit shouldn't be worth anyone's time.