Hello all, after 5 days of searching, posting on various wordpress forums, emailing different posters and plugin makers who commented on the subject, I've come to the conclusion that this plugin or option just doesn't exist and it would be past the abilities I have to attempt.
The idea behind the plugin, is that an administrator is able to close registration to the public, only allowing invited members/commenter's to join. Think of Gmail invites, WordPress invites, Gawker Media blog invites.
The admin sends out membership invites to trusted commenter's/users with unique URLS/hash IDs(?) enabling those users to register at the blog with full commenting abilities. The possibility is also there for certain trusted commenter to have an additional invite to forward to a trusted friend. Thus slowly growing a controlled user base of referred and trusted commentors.
As I said above, the many Gawker Media blogs are doing this quite successfully from what I'm told (see: http://www.kotaku.com/gaming/announcements/kotaku-comments-faq-130964.php). I personally think this would be a huge addition to the vast array of WordPress plugins and would also help quite a few other people who are looking for a similar system to their blog.
Hope there someone out there with an idea of how to create this.