This is a really long post, I apologize if you read the whole thing.
Palpatine somehow cheating death or returning from beyond the grave cheapens everything that both Luke and Anakin sacrificed and worked for in the end of ROTJ. I would have a hard time liking something that undoes the pivotal moment of the first 6 films.
Palpatine possessing someone else through some kind of artifact is a straight-up rip-off of the video game Jedi Academy when the Sith Lord Marka Ragnos does the same thing to the game's big bad Tavion.
If you've read the new canon book Bloodlines, Leia's secret that Vader is her father gets revealed in an extremely public way while Ben Solo is out touring the galaxy with Luke looking for Jedi artifacts or something. They don't show him finding out, but he does find out that way. Why neither she nor Luke bothered telling him before that (he's about 15 years old when the revelation happens) I have no idea, but it clearly affects him. In the novelization of TFA, Snoke and Kylo talk about Vader's weakness and how it cost the Empire everything when he turned against Palpy.
Those 2 pieces of info, neither of which is obvious if you haven't really delved into the stuff outside the movies, could make for a plausible situation in which whatever remains of Palpatine uses whatever the plot is to lure Kylo Ren to him, hoping to revenge himself against both Luke and Anakin by making Kylo Ren into what he had always wanted Vader to be - the ultimate Sith, indestructible, un-turnable. Maybe this version of Palpy even cuts him the same deal - learn from me and I'll teach you how to live forever.
Perhaps you see a Palpatine-powered Kylo Ren just going berzerk with the Force, killing his own Knights of Ren and members of the Resistance (preferably cutting Rose's head off), and being pulled back to the light by apparitions of the people who loved him most in life - and a cameo by his grandfather pre-Vader.
That would be a huge crowd pleaser of course, Anakin, Luke, Kylo, and Palpatine all on the same screen, and could also be comedy gold like this:
Ghost Luke: "You won't corrupt him. He has too much of his father in him."
Ghost Palp: "You mean the father he ran through with his lightsaber like a knife through hot butter?"
Ghost Luke: "Oh yeah, I had the Force turned off at that point."
Ghost Anakin: "We meet again, Sheev. The last time I was but the learner, now I am also blue and glowy."
Ghost Luke (snorting laughter): "Are you seriously telling me his name is Sheev?"
Ghost Palp: "You are no match for me. Lord Kylo will be more powerful than either of you!"
Ghost Luke: "I really wish I had a time machine right now to go back to the Death Start so I could say, 'You've failed, Sheev. I am a Jedi like my father before me."
Ghost Anakin (giggling uncontrollably): "One time on my Star Destroyer, when I called him on the holoprojector, Captain Needa bet me 5,000 Republic dataries that I wouldn't say "What is thy bidding, Sheev?" He zapped the bejesus out of me with his Force lightning, but it was so worth."
Ghost Palp: "Silence! At least I didn't grow up with a girl's name." <imitates Padme> "Oh Ani, you're so brave the way you murdered all those Tusken women and children!"
Ghost Anakin: "Uh, did you see her outfits back then? I was hitting that from Geonosis to Mustafar and back. She could have called me Jar Jar for all I cared as long as got busy with me. What about you, Sheev? You ever even seen a girl naked in all your years? And don't say Mara Jade, cuz that canon is gone."
Ghost Luke: "That hurts, dad."
