I would to set up a system where each page has an owner. This owner can then assign access rights to the page. In the first phase, all I really want is that the owner can specify who can edit the page. In fact, for the start, it could be as simply as an on-off switch where editing it allowed or not.
I think you can hack this patch (http://meta.wikimedia.org/wiki/Page_access_restriction_with_MediaWiki) to achieve that. But sure dokuwiki, for example, has a better security model for that ->http://opensourcecms.com/
Jejc.