I think this exchange of ideas is very good. I hope it can evolve and help create a really secure access control system for MediaWiki.
I'd like to state that PageSecurity protects a lot more operation than Group_Based_Access_Control does. I couldn't find any other extension that implemented all the security features I needed. This is the list of other extensions that I evaluated prior to deciding to build one from scratch:
http://www.mediawiki.org/wiki/Extension:PageSecurity#Alternatives