Significant progress

modules/unfree/default.nix

@@ -0,0 +1,18 @@
+{ lib, config, pkgs, ... }:
+
+with lib;
+let 
+  cfg = config.modules.unfree;
+in {
+  options.modules.unfree = {
+    enable = mkEnableOption "unfree";
+    allowedPackages = mkOption {
+      type = types.listOf types.str;
+      default = [];
+    };
+  };
+
+  config = mkIf cfg.enable {
+    nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (getName pkg) cfg.allowedPackages;
+  };
+}