Early intel for Rogue One was adamant about the film having nothing to do with the ongoing animated series, Rebels, but now that seems like a bit of misdirection, for a few reasons.
First, it looks a lot like the Rebels ship Ghost is spotted among the fighters during the film's final battle, indicated by the unique pattern of lights on the rear of the ship. There aren't too many ships' butts that look like a surprised clown, but the Ghost is one of them. Second, the name "General Syndulla" is mentioned, and unless "Syndulla" is the "Jones" or "Smith" of the galaxy, that would have to be Hera Syndulla, the captain of the Ghost.
Some viewers have also speculated on the use of the name "Blacksaber" as one of the Empire's projects, mentioned as Jyn is searching the archives and just before she lands on the file she's searching for, "Stardust." While there are a lot of sabers in the universe, the darksaber is an ancient Jedi artifact once stolen by the Mandalorians and then wielded by Darth Maul, and yes, it has a black blade. "Blacksaber" could refer to just about anything, though, from Darth Vader's hellish home, to an undisclosed death weapon, to Grand Moff Tarkin's favorite pie recipe. Time will tell.