I still don't understand why we can't just do DMs a bit differently. I know it's new and not time to do it yet, but wouldn't this work?

1. Send a DM of some particular format, which basically just says "If you want to initiate a DM with me, reach me at npub, and include code "

2. Client derives the new anon npub based on some derivation path, or based on the npub(s) that will be party to do the DM, something like that

3. Recipients client does similar, and sends the message with secret code

4. Both clients use and sign messages under these anon npubs in the DM

Rest of network will only see 1 message from A to B, and will not see any further messages from either party, and will not be able to connect A or B to the derived npubs.