Add back allowUnfreePackages

system/nix/default.nix

@@ -1,22 +1,30 @@
-{ config, pkgs, unstable, ... }:
+{ config, lib, pkgs, unstable, ... }:
 {
-  nix = {
-    settings = {
-      experimental-features = [
-        "nix-command"
-        "flakes"
-      ];
-      auto-optimise-store = true;
-    };
-    gc = {
-      automatic = true;
-      dates = "weekly";
-      options = "--delete-older-than 7d";
-    };
+  options.nixpkgs.allowUnfreePackages = lib.mkOption {
+    type = with lib.types; listOf str;
   };
 
-  _module.args.pkgsUnstable = import unstable {
-    inherit (pkgs.stdenv.hostPlatform) system;
-    inherit (config.nixpkgs) config;
+  config = {
+    nix = {
+      settings = {
+        experimental-features = [
+          "nix-command"
+          "flakes"
+        ];
+        auto-optimise-store = true;
+      };
+      gc = {
+        automatic = true;
+        dates = "weekly";
+        options = "--delete-older-than 7d";
+      };
+    };
+
+    nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) config.nixpkgs.allowUnfreePackages;
+
+    _module.args.pkgsUnstable = import unstable {
+      inherit (pkgs.stdenv.hostPlatform) system;
+      inherit (config.nixpkgs) config;
+    };
   };
 }