I don't think much development was done on this specific plan but some of the same ideas (minus the btrfs dependency) can be found in OSTree and Flatpak.
It's a shame that it has such a steep learning curve.
Lots of folks are against a fundamental rethink. It'll have to be introduced a piece at a time (like with snaps and flatpak).
Hopefully we'll end up with something like nix in the end.