Kylo Ren, as we all presumably now know, wants the past to die; he’ll kill it, if he has to (I’m going to abuse the hell out of this line over the next few months and years, especially in casual conversation, if I haven’t already). Yet his past won’t let go of him. As Luke warns, for Kylo to strike his old master down in anger is to keep Luke with him forever–and since Luke gives himself up to the Force, this lingering imprint could very well be a literal presence, in addition to the figurative presence of haunting guilt that weighed on Kylo through most of The Last Jedi after killing his own father in the previous film.
I’m definitely a fan of a substantial lapse in time between VIII and IX. I wonder where that puts Kylo at the start of the film. Will he be haunted by Luke? Will we gain any knowledge into what sort of communication he has had with Anakin/Vader (if not purely rhetorical)? This reminds me of Cade Skywalker from the Legacy comics of the old EU, haunted by the spirits of his ancestors.
Not that Cade and Kylo are anywhere near directly comparable characters. Cade at least was more or less always an antihero, while Kylo is so far pretty much a villain. Still, it’s something that will keep floating in the back of my mind, and maybe Luke will nag Kylo to confront what he has become in a way he did with Cade.
Still holding out for some literal representation of a spirit taking the form of Anakin having motivated Kylo to turn to the Dark Side, perhaps even warning him that Luke would one day act against him while he was still just a Jedi apprentice. Star Wars at times feels Shakespearean (ahem), and such a direction would echo the ghost urging Hamlet to avenge the death of his father, a path that would spell disaster for the prince and virtually everyone around him.