I just wanted to add my thoughts to the mix. Nice reading here anyways, good ideas, but…

… to me the only way to let’s say finish the Skywalker saga in three short bulletpoints.

Luke needs to survive Episode VIII.
Rey needs to be Luke’s lost daugther, that was hinted at in TFA and I still feel Kasdan and Abrams were going that way until VIII, Johnson and Kennedy derailed everything.
Luke is at least an important supporting character in IX, Rey learns she is a Skywalker (the flashback could show Luke), Palpatine is still the bad guy wanting Revenge and in the end Rey owns the Skywalker name because she simply is a Skywalker and Ben should either save / help Rey and / or survive.

I don’t have a real idea how to fix that, but Deepfakes, alternate footage of Hamill and some major retconning within the movies VIII and IX seem somehow possible with the given technology and the fans’ commitment.

Just my quick thoughts.