Cooperative unmixing is only really voluntary if the people participating in the unmixing are anonymous. Otherwise you have known and non-anonymous individuals facing the charge of obstructing a police investigation. Though I will grant that it has the possibility of delaying investigations through multiple jurisdictions, not unlike the Tor model. Tor however is always pretty clear that participants are expected to not maintain logs, for a reason. So the question is why do we want to move away from that model? You have to ask what is so different about finance verses information that we suddenly give up our resolve to allow people freedom.

No-one talks about co-operative unmasking for Tor operators "just in case" we want to trace a crime committed over Tor that the community can agree on.