Right now Python simply does not work at all. I was trying last night just to get the compiler to build, but ran into some Fil-C panics at the last moment when it tries to "freeze" some modules? But it should work.

My idea is to move towards defining Fil-C as a "platform", meaning it would have its own ABI value, so it would look like a target called "x86_64-unknown-linux-filc", and then the magic of Nixpkgs is that it can instantiate a full realm called "pkgsCross.filc" which automatically has every package, whose packages are built on your ordinary non-FilC platform as a cross compilation.

When that works—I hope it works, I probably need help to get it working—you should be able to use all the Nixpkgs packaging helpers like

    pkgs.mkShell {
      packages = [
        (pkgsCross.filc.python3.withPackages (pypkgs: with pypkgs; [
          pandas
          requests
        ]))
      ];
    }

This is already how Nixpkgs can have a pkgsCross.musl that builds everything with Musl as a cross compilation. So it seems reasonable and possible. It should be of wide interest for Nix users, since it would suddenly allow memory safety for whole swaths of the C/C++ packages, it would let NixOS use memory safe builds for core services like OpenSSHd, and so on...

I should probably try to gather some interest among people who are truly familiar with Nixpkgs cross compilation...