Information is thin on the ground for Star Wars Episode VIII. There's a few leaked set photos and the cast are able to say that the script and Rian Johnson are great, but that's really the end of it. I myself have had conversations with several people linked to Lucasfilm and the production in the last couple of months, but their lips were sealed tighter than a Death Star blast door.
Well, now we have something good! Last night, at the UK Gala Screening of Secrets Of Star Wars: The Force Awakens - the making of documentary that will accompany the film on home video (it's excellent by the way, really capturing the love and craft of the production and containing some really exciting snippets) - John Boyega was there to introduce and, while when talking about Episode VIII he did mostly just say that the script and Rian Johnson are great, he did drop a pretty exciting nugget; when talking about new things to be excited, he said Kelly Marie Tran is Episode VIII's "new lead".
Tran, previously best seen on College Humor, was announced to be in the film back in January, but how she'd fit into the plot is a closely guarded secret; there were rumours around the release of The Force Awakens that Episode VIII's script was being readjusted to better focus on the newly introduced characters, leading to some new female parts being reduced, although Boyega's comments suggest things aren't as Light and Dark as they seem; she's important enough to class as a lead.
I'd guess she's going to be somehow linked to the Resistance, given that she's been interacting with Finn. Of course, that's speculation; all we know for is that John Boyega thinks she's going to be great. And he'd know; casting an unknown in a key role worked better than anyone expected with Daisy Ridley in The Force Awakens, so it looks like Lucasfilm are trying to have Force lightening strike twice.
Joining Tran are Benicio del Toro as a rumoured villain (the actor has disputed such evil labelling, but Adam Driver's said the same about Kylo Ren) and Laura Dern, whose role remains a mystery (Rey's mother, perhaps?).
Star Wars Episode VIII is in cinemas on 15th December 2017.