Good approach and drafts, John.

From my point of view the version control should be much less present in dialogs and be more a backup system than a version control. Especially in some situations like lossless crop a backup can be very important and essential to prevent the user from image loss.
By default, the backup could be set to "Keep one backup file" when saving. This default might be changed so that you have a specific or even unlimited number of versions. Also, it might make sense not to overwrite an existing backup with a new backup, so the backup would be always the original.
The backup approach would keep things simple and automatic, (power) users could still change the backup setting and thus make the backup work like a version control.
Just my 2 cents...