made some progress

modules/nixos/desktop/default.nix

@@ -0,0 +1,37 @@
+{ lib, config, namespace, ... }:let
+  inherit (lib) mkOption mkMerge attrNames filterAttrs;
+  inherit (lib.types) nullOr enum bool;
+
+  cfg = config.${namespace}.desktop;
+in
+{
+  options.${namespace}.desktop = {
+    use = mkOption {
+      type = nullOr enum (attrNames (filterAttrs (n: type == "directory") (readDir ./.)));
+      default = null;
+      example = "plasma";
+      description = "Which desktop to enable";
+    };
+
+    autoLogin = mkOption {
+      type = bool;
+      default = false;
+      example = true;
+      description = "Enable plasma's auto login feature.";
+    };
+  };
+
+  config = mkMerge [
+    (mkIf cfg.desktop != null {
+      "${namespace}".desktop.${cfg.use}.enable = true;
+
+      services.displayManager = {
+        enable = true;
+        
+        autoLogin = mkIf cfg.autoLogin {
+          enable = true;
+        };
+      };
+    })
+  ];
+}