The official title for Star Wars: Episode VIII has been a highly guarded secret, just as The Force Awakens was before it. Now, ahead of any official announcement, it seems it may not have been guarded enough as a video that seems to show an official poster for the film may have revealed the title.
SPOILERS for the title, and possibly for the plot of the film, ahead.
The title on the poster, which also bears the logo for Star Wars Celebration Europe 2016, is Star Wars: Fall of the Resistance. The Celebration logo helps lend credence to this, as it may well have been the plan to reveal the title at the convention. The con takes place in London in July, and is expected to have many major revelations and teases, with panels planned for Rogue One: A Star Wars Story, Star Wars Rebels, and everything else under the Star Wars sun(s).
The subtitle certainly makes sense. With actors John Boyega, Daisy Ridley, and Oscar Isaac recently teasing a "darker" story, and following the Star Wars formula it makes sense as well. After all, the start of the Clone Wars and the series of disasters befalling the Rebel Alliance in Empire do offer a track record or pattern for second films in the franchise.
Narratively, we left the Resistance in an odd state of flux. Sure, they'd destroyed Starkiller Base and found Luke Skywalker, the last Jedi, but the ruling organization of the New Republic had been wiped out, with several planets full of people. The loss of Han Solo, Finn recovering, and Rey going off to find her destiny leaves the Resistance fairly open to attack. Meanwhile, the First Order was ready to regroup, with leadership like Supreme Leader Snoke, Kylo Ren, General Hux, and somehow apparently Captain Phasma all making it out alive, and set to come back together.
With the leak, Disney/Lucasfilm may make an official announcement sooner than July, but we'll definitely hear more about Star Wars: Episode VIII at Celebration. No official comment has been made by Disney or any of their representatives.