I am currently working on an extension allowing users to collaborate within managed groups.
At its current state, users can set their pages and/or files not publicly readable using the MediaWiki read right. (only viewable by the page creator). The "classical" rights (edit, move, upload...) work has usual.
This extension is based on AuthorProtect by Skizzerz.
It will be a part of the Seizam project (you can follow it on our -> blog <-).
It will be released under a public license once complete. For the moment, it is working but experimental, and I want to avoid forking AuthorProtect. I can send you a copy of the current code if requested.
You can contact me using this discussion page -> here <-