WMG / Black Sails

Silver and Max will eventually get together
In the original novel, it's mentioned that Silver is married to "a woman of colour" who he leaves to manage his inn when he ships on the Hispaniola. The first episode of Black Sails shows Silver and Max as partners in crime; why shouldn't they end up as partners in businessnote  as well? It would tie up a neat piece of mythology and, more importantly, it would prevent Max from falling victim to any of the many death tropes which probably already have her in their sights.
  • Season 3 seems to have jossed this with a heavy dose of ship-teasing going on between Silver and Madi, Mr. Scott's daughter. We'll wait and see, though.

John Silver is Mephistopheles.
His apparent role in the plot is that of the naive newcomer, an Audience Surrogate providing an introduction to the world of pirates. Except that his actual role is to tempt the other characters and bring conflict to the surface. He tempts Max into turning her back on Eleanor, without her even realising that's what she's doing. He drives Flint to ever-greater secrecy, turning the crew against him until he's forced to murder his best friend. He persuades Eleanor to help Anne and Jack become traitors to their crew. He leaves a trail of dead bodies and broken relationships in his wake, and comes away with clean hands and a ready smile.

It's actually the "old sea shanty" Billy Bones is singing at the beginning of the book ("Fifteen men on a dead man's chest/Yo-ho-ho and a bottle of rum"), and at some point in the series we'll hear somebody sing it.
  • Almost certainly true, if you sing those lyrics from the book along to the music, they fit the melody very well.

Max will turn out to be Mary Read
She has a steadily evolving relationship with Anne Bonny, and Mary will have to turn up sooner or later.
  • There's an interview on youtube with Clara Paget and Toby Schmitz where they're asked about the possibility of Mary Read showing up. The way they talk about it implies that Read would be a separate character from Max — they'd like the dynamic in the relationship to be different from the dynamic between them and Max. Of course, they're not the writers, and supposedly the only people on set that can get backstory out of the writers are Toby Stephens and Zach MacGowan, so who knows how it will develop.

One of the main characters will be the real author of "A General History of the Robberies and Murders of the Most Notorious Pyrates," published in (1724).
I think Rackham, but that's just a guess. I was curious about Woodes Rogers' line to Jack in episode 3x06, that if he wants to control his story he should write a book. The line just stood out to me, like wink from the writers. Turns out the earliest, most famous, and still the primary source of information we have about this era of piracy was written anonymously, with the stated author, Charles Johnson, universally believed to be a pseudonym. This book is where most of our information about Calico Jack, Anne Bonny, and Mary Read come from, not to mention Charles Vane and Blackbeard. As obsessed as Jack is with his name and reputation, this would be a perfect ending for him (especially if Anne is right there with him, making sure he make her look like a badass too).

The show will end just as Treasure Island begins
Right before the final credits role, we'll catch a glimpse of Jim Hawkins in a Flash Forward to the opening chapter of Treasure Island.