I have now written a total of about six thousand words on five fairly concept-heavy subjects (linear algebra, parallax and cepheid variables, the gold standard, the normal distribution/Central Limit Theorem, and complex numbers), There are a couple of observations I would like to make.

Although it's fun, and stylistically appealing, to write as if you were talking to a five-year-old, there are plenty of sentences that would be thought of as "adult"-level sentences which require little to no modification. There are a lot of words in the top 1000 list. Also, there are specific words I find myself trying to use over and over again. "Shape", "triangle" and "measure" crop up a lot as far as subjects with geometric interpretations go. I would be interested in seeing a log of all the forbidden words that crop up across all users.