Great news! This coincides with a few rumors I read about the name "Black Flag". The pirate era was JUST BEFORE the American Revolution time period and it's quite possible since the English and Spanish were dominate forces in the area that Ubisoft will give us an English or Spanish Assassin.
I think this makes for some real good possibilities! Instead of traversing a sandbox area like "The Kingdom" or "The Frontier" imagine SAILING around. Able to dock at various islands and discover what's on there.
It'll also be interesting to see who the protagonist is going to be. I'm sure we'll see A LOT of notable pirate characters like Blackbeard, Calico Jack Rackham, Henry Morgan, Anne Bonnie, etc.
It's also possible this will tie some to Assassin's Creed 3 since the Golden age of Piracy was in the mid to late 1600's. We could possibly see the AQUILA and how it got into the Assassins' hands. And a VERY young Achilles (if was born in late 1600's or early 1700's).
The character could very well be John (Jean) de la Tour. Who supposedly trained Achilles and was the first Assassin in the colonies. His age can coincide with that timeframe.