Whether or not bringing back Palpatine is a good idea or not, I do think it will happen. I can see the main villain (Adam Driver?) seeking out what is now called Moraband as he looks to reestablish the sith and find more power to use against the heroes and encountering there an artifact that Palpy's spirit is possessing in some way or even just a ghost (but somehow different to jedi ghosts, maybe just a voice) and the Sidious ghost says he's unworthy to begin with but gives him a chance to prove himself by killing Luke perhaps. This can happen at the end of the film and he becomes the apprentice to Palpatine who himself somehow grows stronger through this act. The next 2 films deal with the aftermath of this. Although I'm reluctant to reference Harry Potter here, I guess it would be similar to how Voldemort was a broken spirit but was helped to return by followers.