What might have been with Kylo as the main villain (and Rey turning/infiltrating):
Someone on Twitter said this is how TLJ should have ended. I'm inclined to agree, it was sorely in need of a cliffhanger and this also may have precluded Palps' return.
Yeah, I can definitely understand that point of view. No matter what variation of the post-Snoke picture, though, I'll never understand the argument that Kylo couldn't have been the main villain in ep9. For one thing, Adam Driver is the best actor in the ST, and one of the best of his whole generation. That type of acting ability should be used to its fullest potential, and should carry the film. Just have a time jump of one or two years from TLJ, say Kylo has grown even more powerful (and sinister) with the Force as Supreme Leader, and let Driver take care of translating that type of credible threat.
The key for me is that Kylo/Ben is the only next-gen descendant of the Skywalker bloodline in the ST. And after Leia is gone, he's the last living one. His character embodies the Skywalker legacy: incredibly gifted with the Force, and the target of evil corruption being tempted with the power to rule the entire galaxy. That's the story of Anakin, and of Luke, with each one choosing different paths. Kylo/Ben could've been the extension of that to see where it would lead.
The Skywalker Saga started (chronologically) with Anakin believing that others were holding him back. After turning to the dark, he sought to overthrow his final obstacle in order to rule the galaxy. Kylo actually did it! He accomplished what his grandfather had sought. Vader's legacy fulfilled! I can't understand how that's not a compelling setup for the final chapter in this family drama.
What I think would've made this a cool story opportunity for ep9 is to use Luke and Anakin in confrontations with Kylo/Ben now that no dark side puppeteer (Snoke) could prevent it. Use that dynamic to ask the question of what happens to a Skywalker when he has climbed to the top using the dark side but doesn't have a compelling reason to be redeemed. Anakin had his son Luke to compel him to turn back to the light. Luke had his father's tortured soul to fight for and keep him from turning to the dark. Kylo/Ben would have all that power, but be on his own. There's so much you could do with that to put a powerful punctuation on the Skywalker legacy.
Bringing Palps back not only potentially undermines Anakin's legacy, but reverts Kylo back to being a manipulated puppet. Why!? I don't get it. The external battle of Leia's Resistance versus Kylo's First Order would be a metaphor for the internal battle of the light side of the Skywalkers versus their dark side. Winner take all and cement the legacy. Instead, we got a retreading of the same ground as the OT, but compromising it along the way (IMO). Frustrating.