Hi! Universal Blue co-maintainer here, here’s the TLDR. You’ve got the basic descriptions right, “Universal Blue” is mostly the parent organization that holds everything in github.
We take Fedora’s Atomic OCI images and customize them for different use cases (Aurora, Bazzite, and Bluefin) and then publish base images so people can make their own versions of whatever they want. So if you wanted to take Silverblue, Kinoite, and make your own custom image you can mostly just grab whatever you want and shove it into an OS image. Bluefin started off as a “fix me” script for Silverblue that added all the stuff I wanted and then once I was shown what Fedora wanted to do with it the natural progression was to just make it a custom image. We just released 3.0 a few minutes ago actually!
Basically in Fedora 41 the tech will become more widely available with official OCI base images and better tooling. We just decided to start way earlier in the process so we could get all the automation out of the way, build a community, get familiar with it, etc. Happy to answer any other questions you may have!