But you might be able to create it contractually. Before establishing a connection with a node, exchange a sequence of packets whose contents contains an agree

But you might be able to create it contractually. Before establishing a connection with a node, exchange a sequence of packets whose contents contains an agreement that neither node will keep a persistent record of the IP address or any other data or metadata associated with the connection. Refuse to connect a node that does not send a (signed) agreement. It's still tricky about identifying the parties, etc., but it'd be interesting to explore with a techno-lawyercat.