Nix at least is not content-addressable; it's derivation-contents addressable. Under ideal circumstances the same derivation will result in the same contents, but it's not a guarantee.
If you're on a well-worn-path you could operate mostly by lookup and only run the code if something doesn't smell right.
Even if it turns out to be perfect in every way though, it takes a long time for the masses to adopt new languages. I think it might be worth finding ways to build consensus around claims like:
> this particular bit of python can be treated like a pure function
...even though there aren't any guarantees built into the language.