Love your idea for the Knights of Ren! I also think it would’ve given Kylo a more interesting motivation. His motivation for turning to the dark side was never expanded upon in the films, but this would give you the idea that he felt he was doing what was right for the galaxy, even if it was misguided. Him and the other Knights may believe they could control the dark side without it controlling them, but as the trilogy progresses we’d see how it corrupts them.
The Force Awakens novel opened with this “quote” from the Journal of the Whills:
First comes the day
Then comes the night
After the dark
Shines through the light
The difference, they say
Is only made right
By resolving the gray
Through refined Jedi sight
It is an intriguing prologue, but the trilogy never delves into that. Your idea could resolve the “gray” and put the arguments to rest.
For example, I wish Luke had a moment in the trilogy to give some spiritual speech that was on the same level as Yoda’s “for my ally is the Force” speech. You could’ve had Luke explain to Rey why Kylo’s philosophy is wrong in an interesting, optimistic way. I think it’d still be nice to show how Luke’s Jedi Order might be different than how it was before, how he “resolves the gray”, but with an answer that isn’t “Grey Jedi”.
Really, the ST could’ve posed an interesting question and theme. Okay, Anakin brought balance to the Force, but what does that mean? And how do you maintain it? That question could’ve not only applied to the state of Jedi and the Force, but also to the state of the New Republic? How do you protect democracy, and keep it from falling to fascism again?
This is a common idea people have, but you could’ve had a simple role reversal and the Imperial remnant could’ve been the rebels, with ragtag stormtrooper militias committing acts of terrorism across the Republic. And Leia could’ve done some politcking, trying to weed out senators who are trying to turn the Republic back into an Empire. Our heroes could be wondering who has stormtrooper uniforms in their closets.
Speaking of which, I picture the ST “stormtroopers” looking more like this.
I mean, this would’ve been cool for the fandom, too. Imagine the 501st having their members make costumes like this. Could’ve had some pretty cool action figures too, and encouraged fans to kitbash their own stormtrooper figures. I think it narratively makes sense to see how the Imperial element has regressed and become more extremist in the wake of their defeat.