Amethyst's new DM model will allow users to backup their outgoing DMs to a separate Nostr pubkey. If somebody gets access to the main key, they won't be able to find or even count your outgoing messages.
That will create a new class of micro apps to manage DM backup and recovery.
To recover DMs, the backup client re-signs all past messages to a new key your main client just created. If you have two or three clients, you can use 2-3 DM keys. The backup client can keep forwarding your own backed-up DMs to 2-3 other keys so that all clients can sync and see the same messages.
There are lots of interesting features of this model. The most important one is that when re-signing, the date/time of the original message doesn't need to be shown. The backup client re-signs everything as of today.
The public doesn't know these are DMs and doesn't even know if the public date is relevant or not.
Want to know more? Here: