You can already use the cascading permission system to allow stewardship of certain topics.
It'd be nice to allow anyone to submit an edit, but to have the steward/admin review it before it becomes public and approve/deny it.
This would allow a much more functional wiki and would support much higher quality wiki content.
It would also make MojoMojo much more useful as an organizational document system, as different groups / departments could manage their own information / keep control of it, but still allow information to be added with review)