I think the simplest solution would be to implement a password prompt in DC-Desktop before adding an additional device and to encrypt backups in all versions. The latter could be done like in Threema for Android. Users would have to choose a password before each backup, which would then be used to create an encrypted ZIP archive.
In my opinion, changing the name would be a very simple measure to strengthen security awareness and at the same time highlight a feature that not every messenger has.