It becomes very hard to ensure you are being paid properly in his proposed scenario, I would personally expect it would create even more controversy, or extremely long payment records every month for artists.
For instance say we have 500 paid users. Lets call them user1 through user500. Each user listens to the same number of songs a month as the value following the word user in their name. Then we have 500 different rates at which artists are paid for their song playing ranging from the entire monthly fee to 1/500th the monthly fee. Therefore providing a full accounting of each of those rates would be necessary for an artist to understand why they got paid more the month they had a single play than the month they had 400 plays.
To be fair assuming the minimum song length on Spotify is 30 seconds this record provided to artists would have a max length of (31 * 24 * 60 * 2)+1 = 89281 items for premium users plus items for add supported users if they did not overlap exactly in rate. Assuming all Premium users paid the same rate, which is not the case.
Edit: I ignored the 0 listen use case, as well as spotify's 30% cut to simplify an already complicated 'simple proposal'. I also forgot to account for daylight savings time in which a day can have 25 hours.