I’ve heard conflicting reports of Lucas’s treatment and how much of it was used.
Way back when, I thought Arndt’s draft was based off the Lucas treatment, and then Abrams and Kasdan’s draft was based off the Arndt draft. But then I soon learned that Abrams and Kasdan pretty much jettisoned Arndt’s draft and started from scratch. Until very recently I was sure that was the way things went down, but now I don’t think was the case at all. My first hint was that Arndt got screenwriting credit on the film, which meant that at least some of his draft made it into the final film. Then I also noticed he’s listed as an associate producer in the end credits, and he did a Q&A about the film with Abrams and Kasdan where he talked about the development of the script and it sounded like his version wasn’t too far off from what we got. Now, after skimming through The Art Of book, it appears much of what was in the Arndt draft made it into the film in one way or another, and that Arndt and Abrams were very much working together for a good stretch of time to develop the story. Some things are more or less the same, though a lot of things in the final version have simply been developed out of ideas in the Arndt draft. It sort of leaves me to wonder why Arndt left at all (since I had thought it was just because his version was completely different), and I can only imagine it was a too many cooks situation with JJ wanting to write and also to bring in Kasdan.
But where does this leave the Lucas treatment? Well it seems like LFL threw it in the trashcan right away. I don’t know if it was terrible or what, but it sounds as if the Arndt draft had nothing to do with it.