There's just one problem with your model. There's no royalty difference between a Spotify subscriber playing one song vs 1000 songs if it's just % of subscriber's listening time. Someone who gets more plays by absolute numbers is going to be upset when they don't get a proportionate amount of money. The only way to make more money on Spotify is to get more fans and/or convince your existing fans to listen to fewer artists.
This is a popular HN suggestion for disbursement but it makes the math super weird.
This isn't likely to happen or change, but what if subscribers were instead billed by usage? If you streamed 24 hours a day for the whole month, that could round out to $10 a month, but if less, then simply a proportional percentage.
Spotify would never forgo current profits from flat monthly plans, but then why shouldn't artists be granted the same advantages in royalties proportional to a subscriber's ratio of playtime if the subscribers are charged a flat rate any how?