Rey will destroy Palpatine in E9
This is my theory, anyway.
During the course of this movie, our so-called "heroes" (except Lando, who IS a hero) will discover that Palpatine survived on the Death Star II, and that it will actually be up to Perfect, Flawless Rey(TM) to destroy Palpatine where Anakin and Luke failed, making HER the ultimate Skywalker. Luke will show up as a Force Ghost at some point to state that in his meditations in the Netherworld of the Force, he discovered Rey's true lineage, that of a Skywalker, so that will be that mystery solved.
It will be perfect for SJW Lucasfilm, Kennedy, Johnson and Abrams, and a rallying cry for feminists and Identity Politicians throughout the world, that "a female heroine CAN beat everyone else", despite Rey being badly-written and developed. They will practically worship Rey as a Goddess, in fact.
In the meantime, they will have accomplished Kylo Ren's mantra in The Last Jedi, saying "let the past die, kill it if you have to" by doing the above, and at the same time alienating enough of the original and even prequel Star Wars fanbase to disown and walk away from the franchise in droves, leaving Star Wars to be the new poster girl for Feminism, Identity Politicians, Diversitarians and plain old Social Justice Warriors, and in the end, Star Wars will be just for them. As they wanted from the start. And the shill critics will laud the movie as the best ever Star Wars, whilst finding further ways to shut down dissenting comments.
It's really the perfect plan.