The more I think of it the more I like the idea of bringing Palpatine back in some way (though not this way). If the ST is all about legacy, and the OT heroes all find the strength and confidence in their proteges to move on knowing the galaxy is in good hands, wouldn’t it be interesting if the antagonist is an old villain who absolutely refuses to move on in any way?
I think a simple way to have gone about this would’ve been what Matt Smith’s rumored role was to be, to have the spirit of Palpatine possess a host body, rather than have his literal body still be around. To be fair, it almost seems like his spirit is attached to his dead corpse, the white eyes make me thing that’s the idea, but it still a stretch to think his body remained in tact enough to extract from the ruins of the Death Star.
Something I honestly liked from Trevorrow’s script was Hux collecting lightsabers and other Jedi/Sith relics. I could see how his rivalry with Kylo Ren makes him wish he had that power to oppose him. You could’ve tied both things together by having Palpatine’s spirit calling out to Hux (maybe from Vader’s helmet aboard the Finalizer), and offer Hux unlimited power in return for being his host. It just ties into their rivalry well and after how much Hux was thrown around in TLJ, I could see him selling his soul to try and overcome Ren. And between them and the final confrontation, we could see Hux’s body become more like Sidious’ as the dark side quickly corrupts him, essentially destroying his body, and then Palpatine could throw him away and jump into a more suitable host.
That’s an interesting idea with Hux. Personally I’m not sure how I feel about Trevorrow making Hux a force wannabe. Personally I like the idea of Hux as the symbol of the First Order as an institution and would personally keep him separate from the force stuff and have his story be more about the First Order’s fascism and kidnapping kids and all that.
On the force side, I think there’s a real missed opportunity with the Knights of Ren. I would have gone more the Trevorrow route there and made them the big antagonists, with a single figurehead. They were mostly a blank slate that they could have done anything with, which some people would say is not a great place for the final antagonist to be unestablished, but if you really went all in on making them be the dark side of Kylo Ren made manifest - a foil for his struggle - and had them be Luke’s other students, I think it’d totally work. Ultimately they should have formed Kylo’s main ideological conflict. At the end of TLJ, he’s gone full “kill the past” mode. But prior, he was worshipping Vader. If you made the Knights essentially Sith worshippers who want to restore that former power while Kylo wants to move forward and make something new, you’d have an interesting conflict right off the bat (and a place for the Knights to end up siding with Hux who wants to restore the Empire). Then you could work in Palpatine by having the Knights want to resurrect Palpatine and then one of them becoming his host.
Now one thing you bring up which is an interesting idea, is not actually seeing Palpatine’s old body. On the one hand, this would have felt somewhat fake and disappointing (‘trust us Palpatine’s spirit is definitely in this guy’s body’), but what if like you said, when his spirit takes over somebody’s body, their image becomes corrupted as well, and they don the exact facial melted makeup that McDiarmid did (and his voice too)? That’d suggest that the melted look really is Sidious’s true visage, and perhaps even that Palpatine was a separate person and merely a host for the dark lord as well.