Really it seems everyone's theories are a variation of that point. Weather Palapatine is back for real, force apparition or giving orders from a hologram/holocron like I mentioned (which he has already done in canon). Another theory could be that much like the FO uses names of officers from the Empire to show position (Hux has Tarkin's name on his Uniform) Perhaps these "Sith" troopers are just named as such in honor of the Sith
<cocks head to side>
What?Sounds like the most logical reason, Rey is being all Jedi so adopting another negative identity would fit Kylo - 'well if you're a Jedi i'll be a Sith like Papa and finish what he started!!' basically sending him full circle to where he began in TFA.
I think he would have been driven more by the aspect of the fact that the Sith historically have the strongest connection to the dark side and are also the greatest terror the galaxy has ever known. If you're going to usher in a new terror based regime, that should have been the most likely method.
I suspect this is more the case though, probably named Sith troopers for psychological impact on both sides. Much like the FO as a whole, its a shallow adaptation of the Empire it sprung from.
Also the red colouring is just like Snoke's (curiously useless) body guards - but look a lot cooler for sure. I don't think introducing a Palpatine come back in the last film of the trilogy would make much sense...but then neither did Snoke to begin with...
I'm still leaning toward the idea that they are simply troopers, the Sith name just identifies who they're working for. Like how we rarely ever here the full name
Imperial Stormtrooper. What other stormtroopers did we have in the OT?
I'm also more inclined to believe that the red armor of the would be Praetorian Guard was just another cheap ripoff; a throwback to the Imperial Guard of the Emperor. But I do agree, despite the ostentatious color, the lines of the paneling are very appealing to my eye.
As far as D. Sidi, it actually is like the
only option they have. They killed off the last big bad guy before we even knew anything about him, or the extent of his power. Sidious is already a known villain and doesn't need explanation. So he can be reintroduced and defeated within the span of a single film. I'm not holding my breath for anything spectacular beyond it being the end of the worst SW trilogy ever and the fans riot for the OC to be reinstated. <sigh>(happy thoughts)