[Minor49er]

I hope this hypothetical OS never needs to use a swap file.

More seriously, in a time of unobtrusive automated backups and dirt cheap storage space, why is this such an issue where you want to have this kind of system?

[hulitu]

Domain OS had versioning filesystem. You could always load an older version of your file in the editor.

[Minor49er]

Something similar can be achieved today with a combination of autosaves or version saves at the application level as well as time machine backups at the OS level