IMO that page should only be a summary of already defined variables. So, in contrary to windows registry or (shivver) gnome-conf, this should (IMO) only list the variables that are settable in other places too.

I sort-of disagree with that. Wouldn't that defeat the purpose of what sparked this thread? Having the ability to add extra settings will not be possible if you only keep settings that can be set elsewhere. If you're going for this approach, you're doing useless duplication for the most part. The only people who will use it then are people who know the innards of Drupal very well, i.e. Developers or people who've been involved for a long time in Drupal otherwise. Newbies and less technical users won't... If I understand this whole thread correctly, this started with "adding another option would make the interface cluttered." From there, came the idea that new (less frequently used) options could be added to a separate page. Regards, Kobus