[kbenson]

> Malware author provides some evidence that they haven't also uploaded non-encrypted content elsewhere

Any amount of information that could show this would invariably give away the identity of the hacker. Even then, since the information comes from them, it can't be trusted.

> But I think it's a proof-of-concept that shows that there are potentially other ways to escrow ransomed content.

There's a difference between keeping the owner from their own materials and threatening to spread those materials to others. In the first, you at least know whether you get the files back (for the most part, it might be hard to notice small changed/omissions). In the second, not only do you not necessarily know it's been shared, the blackmailer retains the right to spread it in perpetuity (whether it still retains value or not).