This is a very random out of the box idea, but was thinking it could have been interesting if it was revealed that all the Sith troopers were the original clone trooper template from the prequels, Temura Morrison. Probably no way to properly execute it in film other than perhaps giving some of them the clone distinctive audio during the final battle and perhaps finding a way to mention a clone army.
The clearest way to indicate that would be deepfaking all the Sith Eternal officers to have his face. Might have to redub some too.