Why not let people vote it as 'too advanced' for themselves? That way, not only would the articles get ordered in ascending difficulty, but we would be able to see what level of understanding the readers have. Just add a new 'sort by: Ascending Difficulty'.
That assumes beginners know what they know, which strikes me as a poor assumption.
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?