This page is here for historical record. For more info on writing your own GUI Plugins, see the documentation:
One of the things that we are working on with this GUI rewrite is make it really easy to make and distribute themes. We are looking for people to try making a theme plugins, and report any problems, so we can try to fix them.
Here' s how to run the current code: http://puredata.info/dev/PdGuiRewriteTestBuilds
Basically, you'll be able to do everything using the 'option' command in Tcl. http://tcl.tk/man/tcl8.4/TkCmd/option.htm
There are some examples in pd-gui.tcl, and here are some example plugins, you can drop them into pd/startup to use them: