I suspect that there is much to be said by the criticism of the mathematical model detailed in this article. I also suspect there are some simple algorithmic solutions, such as number of downloads in a given period of time – time popularity compression (equates to a greater payout), number of repeat downloads (equals greater payouts), number of on-going and continuous downloads (equals greater payouts), number of downloads that translate into live performance gigs, total number of downloads (all payouts in all categories being proportional profit rates as popularity increases), etc. etc. – that is you would use mathematical models that mimic or equate to the traditional industry musical models and apply them to the new standards in a graduated fashion. The profitability scale would increase over time as the measurement standards are reached and exceeded.
There would be a very logical and justifiable productivity to profitability scale.
Not very difficult to do at all, you just plug in the new equations at the particular rates that make profitability in comparison to the standard industry equivalents.
Just as math pointed out the discrepancies in the profitability models it can be used to formulate new models that either mimic the old models or improve upon the old models.