I think that would be a very useful way to create GUI scenes, eg, window buttons, checkbox, combobox. Label?
It more or less already exists.
http://www.forum.compilgames.net/viewtopic.php?f=4&t=2893
Not sure if this is what you really expect (maybe a system more close to unity3D GUIstyle and GUIskin? ).
The extension will be updated nex week for the last GD version.