I had the thought cross my mind today:
Why doesn't Wikipedia upgrade its revision control system to something more along the lines of git or mercurial, where the database is held in a distributed manner, as opposed to a centralized repository with only one line of history.
In this manner, the core content would be write-only by trusted staff. When users want to make edits, they pull the source of the page, modify it and commit their changes, and then submit a pull request to the trusted staff, who could then review and merge the changes into the main branch.
To some extent, this exists through user pages, where the source of a page is cloned and modified within: wikipedia.org/username/wikipage, and then copied back to the original page when done, but it lacks the benefit of being able to merge other peoples' changes between when the cloning and copying back occurs.
Going to ask my wikipedia-inclined friend about this...it's possible that it might generate too many edits for the staff to approve, but it could at least be held as a model for the more controversial pages.