Currently, if any change is made to the build package script, e.g. adding an extra newline in installPhase, then the package and all of its dependencies will be rebuilt because the derivation hash changed. With an intensional store model, only the package will be rebuilt, and the dependencies will remain unchanged, reducing build times.

http://nixos.org/~eelco/pubs/phd-thesis.pdf refers to a "prototype implementation" of the intensional store, which appears to be in https://github.com/NixOS/nix/tree/secure; maybe that could be resurrected and merged?