Thanks for the feedback Des. I'll have to think about this a bit more but this could be a good idea, even though TKLBAM was never designed for this specific usage scenario. It's impractical to satisfy all usage scenarios with a single, well designed tool, but if with a modest change we could provide system-level syncing capabilities that would be worthwhile.

Note however the implementation would be a bit more involved than you seem to suspect. TKLBAM stores backups on S3, which doesn't support the rsync protocol natively. Also, we use Duplicity on the back-end and Duplicity doesn't have support for this type of caching, though it may be possible to get around that without diverging more from the main Duplicity branch.