Most of the discussion here is missing the point. The actual subsidy is not from unpopular artists to popular artists, it's from (artists listened to by) casual

Most of the discussion here is missing the point. The actual subsidy is not from unpopular artists to popular artists, it's from (artists listened to by) casual listeners to (artists listened to) by heavy listeners. Under the pro rata model, any heavy listeners will divert "other people's money" toward the songs they listen to. This could be a superfan obsessed with some indie band, or it could be a fan of popular artists. Moving to a user centric model will certainly penalize any artists that overindex on heavy listeners. For example, children's music that gets put on repeat will probably take a hit.