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?