I've been talked into formally participating in the W3C Payment Interest/Working Group as part of working on GNU Taler, well my employer INRIA is a member.
Drop me a line if there is anything I can do/say/watch to help keep that potential standard tor friendly.
Best, Jeff
p.s. There are related groups on privacy and credentials that might be of more interest to Tor Browser which I'm not involved in, btw.
p.s.2 Just fyi, Taler is a transaction system based on RSA blind singing. We haven't finished the demo for Taler yet, probably by 32c3 though. Feel free to look at these if you want to know more : http://taler.net http://grothoff.org/christian/taler-draft.pdf