Re: Group Wiki Plugin (not a release, but in progress)
According to your project’s requirements, why do you absolutely need to develop a wiki ? I understand that you want easy writting facilities so why not using blogs ? Of course, there would be a lot to build in the group’s front end but at least you can use WP’s core functions.
1 – link a blog to a group, maybe using group meta (and make it private if needed) and give group users certain rights on blog.
2 – build a front-end tool for groups to be able to view, add pages and create content
3 – the post revisions could be useful to have full history of the page
Of course, work has to be done on user’s roles and capabilities to be able to view revisions and edit contents as non admin users.
This is just an idea, I don’t know if this could match your requirements.