Extension idea. Wiki. Someone can create a new discussion, select a wiki checkbox next to the submit post button, and then any member can edit the original post. But, the original poster could reject the changes.
To keep it simple and to save space, no need to list or view revisions. Instead, the post cannot be edited again until the original poster accepts or rejects the changes. Just one pending revision at a time.
So, not a full featured wiki, just the ability for members to somewhat collaborate.