Mark Hamill is turning out to be the best source of information on Lucas’s proposed sequel trilogy. In an interview where Hamill debunks fan theories about The Last Jedi, he let slip a tidbit about Leia’s part in Lucas’s story:
“[regarding why Leia] didn’t more fully develop her force sensibilities [in the sequel trilogy/outside the movies]…I think that’s something George Lucas addressed in his original outline for 7, 8, and 9. I was talking to him last week…but they are not following George’s ideas.” – Mark Hammil, Fan Theory Exploder
Hamill looks and sounds dejected when he mentions that Disney are not following George’s ideas. Is this a sign that Hamill thinks Lucas’s story was better than the films Disney have made? Perhaps he had a bigger role, or perhaps he’s just loyal to his lifelong friend.
Since Leia was shown to have Force sensitivity in the original trilogy (and of course she comes from the Skywalker bloodline), it stands to reason that she would develop this further in the sequels.
It’s also likely that one or more of the young characters in Lucas’s story was the child(ren) of Leia and Han Solo. Lucas’s focus was on the Skywalker family, after all.
George Lucas's Sequel Trilogy 