Someone who listens 20 hours a week should pay more than someone who listens 5 hours a month on Spotify. Just set a rate/minute and track each user's usage and bill them monthly.
Then pay the same rate/minute (minus a super small commission %) to the artists of whom the music was streamed.
This would mean that artists get a fair share for what they contribute. If Madonna releases a new album which is a flop then why should she still get the same payout as her last album which was a hit? Equally, if a new artist releases a real banger why should they get less for their talent only because their name is less established as someone else?
This model would also allow a platform like Spotify to push the rate/minute slowly up until they reach a point where demand and supply meet happily. We would be able to find the real value of good music which consumers are willing to pay.