I've wondered if there would be 2 Features possible for the GUI-Editor:
1.) Positions are stored relative, not absolute. If that's already in, forgive me, I did not look close enough.
2.) When saving a GUI, IDs get exported to a .h File to be included to the project's source. Naming of IDs should be added.
I would add this and contribute, but I am not yet good enough with Irrlicht to do that.
rya.