It would be lovely to see Bittorrent in this space. Distributing an identical blob to N machines is squarely within its wheelhouse. All those CI machines would make wonderful seeders too.
As far as I know there aren't any projects doing peer-to-peer distribution of container images to servers, probably because it's useful to be able to use a stock docker daemon on your server. The Kraken page references Dragonfly [2] but I haven't grokked it yet, it might be that.
It has seemed strange to me that the docker daemon I run on a host is not also a registry, if I want to enable that feature.
It's also possible that in practice you'd want your CI nodes optimized for compute because they're doing a lot of work, your registry hosts for bandwidth, and your servers again for compute, and having one daemon to rule them all seems elegant but is actually overgeneralized, and specialization is better.
Steam never used P2P downloading but they've had deals with ISPs and communities really early and made their own "CDN" full of caching servers everywhere, so if you waited a few hours to update, it might make it to your local server in time. Now I think they're on Akamai as well.