Sounds good but need a device to device DM history transfer type situation like you do when setting up Signal on a new phone.
Discussion
Even if that opens many opportunities for security breaches no matter how well implemented?
Look at signal as a case study, has there been many breaches with their design? You can only have dms on one device at a time, transferring them deletes them from the old device.
You can have dms on 1 cell phone and 4 additional devices with signal. Messages are available on any/all devices from the moment each device is linked (no backwards history available)
Sure, but Nostr can't keep your DMs in your phone only (relays and the other party have it and can prove it at any point in time).
We have to address security in a different way.