Music subscription is definitely increasing in success each day, as well as similar video services. It's just a shame that most of this comes in separate applications.
My vision of J Rivers approach on this would be:
1. Implement Performer in MC14 or 15.
2. Make it possible to access online database and local library at the same time
3. Use different tags to separate online tags and local tags. Would make it possible to tag things like Genre, Artists and albums of interest to easily browse local and online database without the overwhelming number of tracks. A separate online popularity/rating tag with you're own rating on the online tracks would also be cool. A lot of things could be done here, though I'm not sure if it would be an easy task.
I'd be close to heaven with just number 1 and 2 also