keychat on Nostr: If the Nostr protocol supports the re-publisher functionality, that would be ideal. ...

If the Nostr protocol supports the re-publisher functionality, that would be ideal. Moreover, if the goal is to address the issue of relays knowing the sender's and recipient's IP addresses, relay X can also act as the re-publisher. This is feasible because the "ecash stamp" on the outer envelope can simultaneously prevent spam targeting the re-publisher.

One particularly great aspect of this proposal is that it requires both the sender's and recipient's addresses to be one-time use. This is very similar to Keychat's metadata privacy mechanism, where Keychat users have separate sending addresses and receiving addresses that are constantly updated. Currently, Keychat effectively protects metadata privacy at the application layer, and we hope to further promote metadata privacy protection at the network layer in the future (mainly focusing on IP addresses).