At this point in time, I don't think a teaching wiki would be very productive. Wikis work well for topics that can be broken into small, independent chunks. I'm basing this judgment off broad comparisons between wikipedia vs wikibooks. More book-like and structured wikis require more devoted editors, and the strong contributors like Eliezer and Yvain are probably going to want to put their energy into this site for the time being.
The one variation I think does have a good chance of flourishing alongside OB and LW would be a rationalist dictionary. I mentioned this early on, but didn't get any comments then. If a beginner can have a reference for terminology, common phrases, and acronyms, most of the posts should be accessible. It could also be a standard place to post syllabi. OB and LW are the best sources to learn from right now, but they do need a reference guide.
One of the missions of OB/LW is to attract new learners, and it's clear that they are succeeding. But the format feels like a very difficult one for those new to these ideas, with beginner-level ideas interspersed with advanced or unsettled theory and meta-level discussions. You wouldn't play <insert cool-sounding, anime-ish video game here> with the levels on shuffle mode, but reading Less Wrong must feel like doing so for initiates.
How do we make the site better for learners? Provide a "syllabus" that shows a series of OB and LW posts which should be read in order? Have a separate beginner site or feed or header? Put labels on posts that designate them with a level?