Star Wars: Rogue One - 10 Simple Blunders That Would Ruin It
2. Any Sequel Trilogy Allusions
Pretty much everyone loved The Force Awakens and even those who didn't are still excited about Episode VIII because, well, it's still Star Wars. As such there'll be a massive temptation to somehow link this standalone prequel into this wider mythology. Ostensibly this would imbue Rogue One with a sense of greater purpose, but all it'd really do is devalue the base story it's trying to do. Think Marvel, but spanning forty years.
But there's so many ways to do it that it'd be very hard to resist. You could have Palpatine talk about his quest for immortality, bringing Plagueis back into the discussion, or Diego Luna's character be Kes Dameron, or Forest Whitaker be related to anyone. Heck, if we're expanding his character, why not have a scene where Darth Vader laments how he'll never have grandchildren (nudge-nudge). That last example aside, these could all strengthen the film at hand, but it'd defeat the point of expanding the world to have everything honed in on The Force Awakens
It'd be especially perfunctory given that Rebels is already exploring a lot of this wider mythology stuff, with a cross-guard lightsaber popping up and various allusions to the Force outside of Jedi and Sith. Although, on that note, if Rogue One is going to tie into some element of Star Wars, that animation would be it.