Pro or con, I don't care. I just had been under the impression that "midi-chlorians" as a specific word and concept was developed explicitly for the PT, setting aside vague hints that Force-sensitivity was inheritable. Lucas has always revisited his battered notebook for names, planets, ideas. For some reason, he conflates this all the disparate elements in his notes into the idea that he had the whole saga planned out in advance. I have enough experience with the story and development thereof to usually call him on his bullshit. The specific mention of midi-chlorians (using his August 1977 spelling), however, was the biggest surprise in the whole book. Second biggest was the mention of Luke and the Princess being twins at one point in the development. Now obviously, it's not a direct line concept to Return of the Jedi's revelation. It's just another developmental element that was in his notebooks that reappeared when he needed a story point. There's plenty of cites in the book that he never actually planned them to be siblings in the final concept as he originally wanted Luke and Leia to end up together and Han to go away. It just never worked in the eventual storyline of Luke becoming a Jedi so Han got the girl.

This has been a very interesting book and I really hope that they do them on the sequels. His next project appears to be Raiders of the Lost Ark.