Lucas talking about the Force is the most interesting part to me;
At first he just talks about how lightsabers are just regular weapons, but that they are preferred by the Jedi and he gives a pretty standard description of the Force. However when he talks about how “certain creatures are born with a higher awareness of the Force than humans”,he mentions that they have “more midi-chlorians I their cells.” So yes, Lucas did in fact make up midi-chlorians long before the PT, however here it’s a bit vaguer. And it’s interesting that it originates from this “improvisation” session.*
He also talks about how Luke needs “another twenty years before he actually begins to cope with [the Force] on a real level.” He also states that the Force can be learned by “anyone”.(*EDIT: Seems like Lucas has been tampering with this particular part in Rinzler’s book.)
I wonder if that last bit of info will ever make its way here. I’m doubtful, but it may happen.