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