I will just add that I hope that my changes will make it easier for other modules like lesson to use questions from the Moodle question bank (something that has been talked about for a long time). Therefore I key bit to look at is Development:Question_Engine_2:Design#API_for_modules_using_the_question_engine.
Actually, the details of that are already out of date, I was trying out implementing the key parts of this plan yesterday (before finishing writing the design