I think you can fix that incentive issue relatively easily by allowing people to choose the allocation arbitrarily after some sort of minimum tax, e.g.
The first $4 of your monthly sub is divided amongst all artists you listen to based on time spent listening, and any additional money you decide to add to your subscription is distributed to artists as you see fit. You can elect to use the same distribution algorithm as the first $4 of your subscription, use the same algorithm with different weights (e.g. your favorite artists listen time is doubled before payout is computed) or you can choose to have an arbitrary percent of it go to whatever artists you want, even if you don't listen to any of their music. Spotify already has to have a payment engine to support paying all the artists anyway, generalizing it beyond fixed subscriptions seems like an organic way to address the issue of unfair income distribution if they were interested in doing so (I don't think they are).
In the above system, the issue of "don't listen to other artists" only comes up if you don't have enough money to give to the artists you want to support, no different than the incentives of "don't buy the CD of artist A or you won't be able to afford the CD of artist B, who you like and wish to support more."
The first $4 of your monthly sub is divided amongst all artists you listen to based on time spent listening, and any additional money you decide to add to your subscription is distributed to artists as you see fit. You can elect to use the same distribution algorithm as the first $4 of your subscription, use the same algorithm with different weights (e.g. your favorite artists listen time is doubled before payout is computed) or you can choose to have an arbitrary percent of it go to whatever artists you want, even if you don't listen to any of their music. Spotify already has to have a payment engine to support paying all the artists anyway, generalizing it beyond fixed subscriptions seems like an organic way to address the issue of unfair income distribution if they were interested in doing so (I don't think they are).
In the above system, the issue of "don't listen to other artists" only comes up if you don't have enough money to give to the artists you want to support, no different than the incentives of "don't buy the CD of artist A or you won't be able to afford the CD of artist B, who you like and wish to support more."