> I suppose it's reasonable that the Nix project doesn't want to host binary versions of lots of old packages to make this use-case fast. In that case, I'd want it to be easy to clone the binary version of those dependencies and source them locally. Maybe this could operate as something like a caching proxy in front of Nixpkgs, that will store my own permanent copy of any package that I access or build.

I don't know when it will be ready, but some work has gone into backing Nix caches with IPFS, and it looks like it could be a really cool solution for making it easy to share a cache for 'extra' or 'old' packages without much infrastructure work on the parts of users.

https://github.com/NixOS/nix/issues/859