I am sorry for this late reply but I had to think some.
What about the following new project?
Currently wikipedia's default editor looks like this
[login to view URL]:BLP_editintro
And the extension for this editor is this
[login to view URL]:WikiEditor
It looks like this.
[login to view URL]:[login to view URL]
But this is not wysiwyg.
Can you make this wysiwyg? for example by making ajax or any other methods?