One thing it had that I thought would be relevant for
@Zyobot's idea was that in that fic being a Sith isn't illegal - so the Jedi can't really act against Vader b/c he's being helpful and not doing anything illegal. That's kind of necessary for the fic, but IMO dark side force use in general, and
particularly being a Sith, probably is formally illegal in the Republic, probably as a law that got on the books during the wars against the Sith empire and never got taken off. Mace Windu and the Jedi go to arrest Palpatine on the grounds that he's a Sith Lord and this is treated as perfectly legitimate in universe (even if it's sometimes presented as not in fanfic). I guess this could be because "being a Sith Lord" makes him a suspect for the Sith Lord who is working with the confederacy, but it also seems pretty likely that being a Sith is straight up illegal in the Republic, given the Sith wars only really ended when the Sith were (supposedly) wiped out. And we never really get any Sith doing the "technically I am doing nothing illegal" thing that I know of, and if they could one absolutely would.
In the Darth Vader + Death Squadron sent back idea, this would put Vader on a much more adversarial ground with the Jedi + Republic.