I have an open issue regarding Python where I think it's worth considering the overall implications for nixpkgs infrastructure.
See the bit under the heading Reducing evaluation overhead.

This is basically an instance of https://discourse.nixos.org/t/1000-instances-of-nixpkgs/17347, just inside nixpkgs.

Python isn't the only ecosystem where the packageOverrides idiom comes and bites us performance wise, but it is the most common source of such issues.