boot = {
    supportedFilesystems = {
      btrfs = lib.mkForce false;
      cifs = lib.mkForce false;
      f2fs = lib.mkForce false;
      ntfs = lib.mkForce false;
      xfs = lib.mkForce false;
      zfs = lib.mkForce false;
    };
    # Make the kernel much lighter to build, otherwise needs 30G+ ram
    kernelPatches = [
      {
        name = "disable-bpf";
        patch = null;
        extraConfig = ''
          DEBUG_INFO_BTF n
          CONFIG_DEBUG_INFO_BTF n
        '';
      }
    ];
    initrd.allowMissingModules = true;

    tmp.useTmpfs = true;
  };

Didn't change the kernel

obstacle to making it all automatic with nix-forecast

I figured the biggest issue would be that it's not easy to map cached store paths back to attr / package names

Also got these to not compile gtk

  nixpkgs.overlays = [
    (final: prev: {
      stoken = prev.stoken.override { withGTK3 = false; };
      alsa-utils = prev.alsa-utils.override {
        withPipewireLib = false;
        fftw = null;
      };
      alsa-plugins = prev.alsa-plugins.override {
        libpulseaudio = null;
        speexdsp = null;
      };
      sdl2 = prev.sdl2.override {
        pipewireSupport = false;
        pulseaudioSupport = false;
        x11Support = false;
        jackSupport = false;
      };
      ffmpeg = prev.ffmpeg_7-headless.override {
        withSpeex = false;
        withOpenmpt = false;
      };
    })
  ];

Also got these to not compile gtk and some other packages

  nixpkgs.overlays = [
    (final: prev: {
      stoken = prev.stoken.override { withGTK3 = false; };
      alsa-utils = prev.alsa-utils.override {
        withPipewireLib = false;
        fftw = null;
      };
      alsa-plugins = prev.alsa-plugins.override {
        libpulseaudio = null;
        speexdsp = null;
      };
      sdl2 = prev.sdl2.override {
        pipewireSupport = false;
        pulseaudioSupport = false;
        x11Support = false;
        jackSupport = false;
      };
      ffmpeg = prev.ffmpeg_7-headless.override {
        withSpeex = false;
        withOpenmpt = false;
      };
    })
  ];

eb:

(
  { config, pkgs, ... }:
  {
    options.nixpkgsNative.pkgs = lib.mkOption {
      type = lib.types.pkgs;
      default = null;
      description = "Native nixpkgs for the system being cross-compiled to get native packages to reduce build amounts";
    };
                                                                                                                         
    config.nixpkgsNative.pkgs = import pkgs.path {
      localSystem = config.nixpkgs.crossSystem;
      inherit (config.nixpkgs) crossSystem config;
    };
                                                                                                                         
  }
)

config.nixpkgsNative.pkgs.mpv-unwrapped

Nice, ty.

I did a similar thing to avoid specialArgs, but with pkgs.unstable as an overlay for nixpkgs-unstable when I needed it downstream for other reasons.