The holy grail of GUI, is a tool which allows you to easily create and extend user interfaces, offering all sorts of things like printing, drag-and-drop, and a good-looking set of widgets/controls/whatever.
The way to get there, is to bring data models to a higher level (a goal of my Data Views work), and to generate the GUI from a more abstract non-procedural description that today's Tk does.
See also Steve Landers' work on KitView at http://mini.net/tcl/2443