I'd argue this would be a lot simpler and cheaper to setup than the byzantine distribution system we currently have in place.

It would also make the economics of streaming viable for the majority of artists rather than the small pool of folk raking in the bulk of the money.

How? The current system is super simple:

revenue * 0.7 = total payout total payout / no. of streams = payout per stream payout per stream * streams of an artist = payout for artist

In the proposed system you'd have to calculate the payout per stream on a per-account basis and have additional complexities like how to handle family accounts etc.

Computers are very good at doing these calculations

Obviously, but as I said it's much more complex and therefore more expensive to do. With a negligible effect.

a) SQL queries are not expensive.

b) As I said, the effect for the vast majority of artists would be quite the opposite of negligible.