Ah, I know Piet Kommers from Int Journal of Web-based communities. That sounds an interesting idea.
I hadn't thought about Moodle forums being blocked - that is an interesting point. Does anyone know if it has happened?
I would hesitate to claim to be in the 'free' world as exaggerated claims about our own freedom might get in the way of understanding our own conditions and that of those with whom we are speaking - but maybe that was another tease Gers

On CABWEB, we have an open network/ community and a closed one - I am not suggesting anything specific for Moodle but think that we should keep an open mind on what might be needed.
Of course we all know, there must be closed forums on Moodle.org (the 'teachers forum' for example). Who knows the Particularly Helpful Moodlers may have their own space, and many other groups.
AFAIK the only way to make a 'hidden' space is to make everyone a 'teacher'.