It includes the following:
> We strive to improve the experience of consuming packages from nixpkgs by providing a layer that records their evaluation, build, and cache metadata. We call this layer - a catalog. This allows users of flox to select from multiple versions of packages. It also enables enterprise users to share packages in binary form without exposing their source code or even their Nix expression.
This sounds in some ways pretty similar to something I'd been imagining for Nix, particularly for the purpose of grabbing package definition sources which have been known to work for a given version or range. (The use case is automatically grabbing or generating packages for given semantic versions instead of by Nixpkgs hash.)
I'm interested to see what all they've done with the catalog, and I wonder if it will ever be brought to Nix proper. If that were likely, they would have been developing this in the open, right? (Maybe not! Getting consensus is hard... I do see that the catalog itself and some related work is up on GitHub.)