I wonder how different things would be if Leia wasn't Luke's sister and he went with introducing a new character in her place.
If that had happened, we would've gotten twelve movies instead of six.
During and after ESB's production, Lucas' original plan was to have Luke's Sister be an entirely new character, one whose identity would be a mystery and cliff-hangar for the third film in the trilogy. At this stage, the plan was to have four trilogies: the original introducing Luke and the Rebellion, a sequel trilogy with Luke on a mythic quest to find his sister while the other heroes built the New Republic, a prequel trilogy about the original Republic's fall from democracy into dictatorship, and an epilogue trilogy about an older Luke Skywalker passing the mantle to a new generation of heroes.
But after the production of ESB taxed Lucas dramatically, combined with the divorce of his wife at the time, he started to lean into the idea about the then-named
Revenge of the Jedi being the "final film" of the trilogy, and far more interested in making the next trilogy go back in time instead of forward. So he scrapped his sequel plans, and cleansed the "search for Luke's Sister" cliffhanger so that there wouldn't be any loose ends, in order to give the film a sense of finality.
He later entertained the "sequel" idea post Ep. III with a treatment involving Maul and Talon, and serving as an allegory for the Iraq War, but canned those plans as well. Elements from his "epilogue trilogy" were what would end up being used for his Ep. VII-IX drafts that he sold to Disney, only for those not be used at all.
Lucas has since stated that every version of an "aftermath" story to ROTJ was going to culminate in Luke passing the torch to a new generation of heroes, part of which would include Han and Leia's kids....stating that the saga was always supposed to be about "the father, the children, and the grandchildren." Which is one of the few things that the trajectory of the Expanded Universe has in common with Lucas' vision for a sequel...but that's a pretty major element.
One that Disney inexplicably opted to depart from by having only
one grandchild for Anakin Skywalker, and then just killing him off to boot.