It would be interesting to have this at Internet scale, everyone on the planet who is building software would share hashes of the code they built, the binaries they built and the compiler details.
https://archlinux.org/packages/community/x86_64/pacman-bintr...
Note, I don't recommend this for haskell packaging on Arch as it slows things down substantially.
We have a company nix cache on S3 overlaid on top of upstream nixpkgs cache where only the CICD is allowed to push/update the cache.
Employee computers are all read-only.
Works great!