Could you explain why you find their encryption scheme 'lackluster'? I'm not seeing that conclusion in the linked document.
> When the above attack model is extended to include multiple clients independently updating the same repository, then Borg fails to provide confidentiality (i.e. guarantees 3) and 4) do not apply any more).
There are some ideas on the issue tracker for fixing this long term (like random nonces, session keys, ...), but that stuff will have to wait until after borg 1.2 (which soon goes into release candidate phase).