I’d also add to the thought about Snoke and the First Order.
“If Skywalker returns, the new Jedi will rise.”
To me the line implies Luke would’ve come out of exile in J.J.'s version of Episode VIII and rebuilt the Jedi Order over the course of the film and possibly Episode IX too. I could see Rey helping too.
J.J. said he was surprised most by and in his own words how dark Luke was portrayed in The Last Jedi. Daisy also said his plans were vastly different from what we got.
We know in George’s Sequels he planned to have Luke rebuild the Jedi throughout the trilogy and equally there’s a snippet of Rick Carter in The Force Awakens behind the scenes documentary talking about as the trilogy goes along that we’d discover the true nature of the Force or something like that. I remember also Kathleen Kennedy saying they merely changed the history and order of George’s ideas but didn’t make wholesale changes. Maybe at the time that was true but it doesn’t always add up either in light of Bob Iger’s book.
It seems to me like there were too many clashing visions and ideas floated around. It seems like they may or may not have originally planned to follow more of George’s plan with the Jedi and the Force through his and J.J.'s ideas. However they decided to let Rian start fresh away from these notes or whatever it was J.J. wrote out. Rian did talk about asking to be given a clean slate from notions J.J. came up with. He was granted permission.
However it seems like he had nobody to reel it all in to create continuity and consistency with The Force Awakens and vise versa. It seemed to be what the Story Group was set up to do but they didn’t bat an eye or notice the inconsistenciess. It ended up being like a relay race instead.
There’s honestly too much misinformation about the process to know what is and isn’t true with what was the plan and wasn’t the plan. The films reflect as much as there’s no real set ups and payoffs that feel earned throughout each of the three films.