Note that RSS 'podcasting 2.0' does have some payment stuff which could catch on, though is not precise enough to automate (micro) payments.
A big motivator for me is that I know I spend a lot on web creators already, but I want to spend money across more creators without necessarily linearly increasing my spend. Managing tons of tiny subscriptions is much harder without book-keeping technology. Having something machine-readable to help with that mission would be great.