It is a part of "layout components" at the
http://labs.jboss.com/auth/wiki/RichFacesFuture list. So, it is #2 between the features that are not implemented yet.
At the same time, we did not refuse the idea to integrate some third party stuff yet. Like this: http://livedemo.exadel.com/richfaces-rex-demo/
Thanks for the redirect, I'll have a look. About restricting 3rd party stuff... A move like that would not let me use RF in my project as our schedule requires that I use components from Netbeans already built and upgrade them to RF in later releases.
My opinion is you're much better off allowing everything and just building superior components.