Wikis are great tools for collaborative content of all types, but the choice for website creators who want a level of collaboration seem to have to choose between a static website, a wiki that anyone (or all members) can edit, or an overkill customized web app.
A simple innovation that needs to propagate through wiki software is adding the ability to suggest edits and accept those edits. Perhaps you want a wiki that anyone can suggest and edit, but only registered users can edit freely or accept edits. Or you want anyone, including members, to only be able to suggest edits, and only have moderators able to approve edits and edit freely. Etc, etc.
Ikiwiki always has some work in this area; there is the moderatedcomments plugin and the
checkcontenthook. The hook allows, for example a plugin to reject changes with spam links or swear words. A plugin could also use it to save the diff for later moderation.
I think the difficulty is in the moderation interface, which would need to apply the diff and show the resulting page with the changes somehow evident (for users who can't just read diffs), and would have to deal with conflicting edits, etc. --Joey