Encrypted database backup (as opposed to unencrypted CSV / JSON) is definitely the essential thing with this request. But I imagine a database backup could also include additional information not presently included in the CSV (password history, URI matching settings, etc. Possibly even attachments - more on this below) adding even more value, and less adjustment, if you ever were to re-import from the backup.
It would be nice to have the option to include (or not) attachments with the database export as well. Since the CSV doesn’t include attachments. Not knowing how attachments are stored (or how difficult it’d be to include/exclude), I’d say that’d be low priority, but nice to have the option.
Also nice to have, but perhaps not necessary, the option to encrypt it with a different/unique password from the master password.