Even if TLJ leaves some narrative threads open, I kind of think it stands on its own regarding the thematic elements it has. Even if we don’t see what happens with Kylo Ren, or we don’t the restoration of the Jedi or the Republic proper, we know there are still people that the fight will continue after the film ends, and they will eventually succeed.
I also kind of like the parallels TLJ shares with Le Morte D’Arthur, where King Arthur story ends with a duel with his wicked kin, Mordred, and the ruin of his kingdom, but there is hope that Arthur will return from Avalon one day and restore the kingdom.
Like Arthur, the OT and these bookends could be seen as focusing on the birth, life and death of Luke Skywalker. Ironically, though, I don’t know if I actually would want to show Luke dying in this version. I like the idea of leaving his fate ambiguous, allowing the audience to choose what happens to him. Does Luke die there on the island and become one with the Force, or will he live on to restore the Jedi Order as Lucas intended to depict?
Kind of the same idea with Kylo. I like how TLJ ends showing Kylo “winning” the battle, but losing spiritually. And the audience is left to wonder if Kylo is doomed to the dark side, or if there is still hope for redemption.
Regarding George’s ST ideas, we know that at some point George suggested combining the Jedi Killer character with Han and Leia’s son. So in some version of his treatment, he still fell to the dark side just as he did in the final version of those films, but we don’t know what his fate would have been in George’s version. So leaving Kylo’s eventual fate ambiguous and letting the audience ponder on it fits with what little we know about Lucas’ version of the sequel trilogy.
And the intentional ambiguity of what comes after mirrors the intentional ambiguity of what comes before the prologue. By having ROTS operate as a standalone film, the audience can be left to imagine a version of how Anakin and Obi-Wan met that is more in line with what the original trilogy tells us: Anakin followed Obi-Wan on a idealistic crusade, and Owen thought Anakin should’ve stayed on Tatooine and not gotten involved.
That’s not really what we see in the actual films, but by not showing how they met and coming in on their story in medias res, the audience could choose to imagine the events before the prologue however they want, whether it be more in like with the OT, or how it is depicted in the rest of the PT.
I don’t think it finishes thematically either. People love the broom kid for some reason but it doesn’t show anything new or inspiring. Ordinary people can be force sensitive? People believe in legends about Luke Skywalker? We knew that already. That was what Rey was about. Likewise Kylo Ren’s story. What is the lesson there? Luke has to learn that certain people can’t be redeemed and he should just abandon them? All the sequels have the same problem of retreading the same ground as the original trilogy and the prequels, and The Last Jedi is no different.
In the sense you’re talking about, every episode could be standalone (the original movie was designed to be but none of the others were.) But it’s your edit, do what you want.