I have not seen this before — some of the Ubuntu people are experimenting with methods based off of rsync/zsync for doing package updates (link).

In other news, I have frozen a copy of the zsync technical paper, for reference purposes. It has been ages since I updated it anyway, so I am keeping a copy as-is before I update it with some of my current ideas. It is important that I get a comparison in the paper with what I am calling structured patching systems: like the new differential Package list updating that Debian have implemented.