I think the dilemma they ran into was Michael Ardnt not feeling the script worked with Luke being reintroduced earlier in the film. Once he came into the picture, Ardnt said that he stole the spotlight, and I’m guessing it hurt the film because the new characters didn’t have enough time to really establish themselves. So, Luke became the goal they were after. But, I think even in George’s treatment, Han probably died at the end of TFA. So the way the story was set up, there were limited possibilities for the big three to share screentime altogether.
It did seem like George’s treatment for 7 may have actually portrayed the Solo son’s fall to the dark side, rather than it being the mystery/backstory as it is in the current ST (but it may have just been flashbacks). But it seems Luke was in a Colonel Kurtz-like exile even in George’s treatment.
I think we can discuss ad nauseum about what-ifs and alternate versions of the ST (people still do rewrites of the PT even now, even I have before) and if it would’ve worked or not. I think, at the very least, it would be cool if we got a flashback in IX of Han and Leia giving Ben to Luke, and it could be an opportunity to have them on screen together but still fit within the story. I’m not necessarily expecting that, but I think people would enjoy that.
I know I’m just setting myself up for disappointment, but I can picture something like that as a cold opening for the movie. Luke has a brief discussion with Han and Leia, and the last shot of the scene would be a close up on young Ben as Luke tells him he’s destined for great things, and then it would hard cut to an older, scarred Kylo Ren as Supreme Leader of the galaxy, sitting on a cold, black throne.