Rare has revealed that once Sea of Thieves is fully released we will be seeing an increase of map size as well as the limit of ships per world increased.
According to Rare Executive Producer Joe Neate, after the launch of Sea of Thieves the game will be updated with an increase of ships per world, as well as a larger scale map. This increase of map size would include "island designs" that Rare already have prepared.
Neate said in an interview with Windows Central that "There are currently three subtly different biomes in the game right now, Shores of Plenty, Ancient Isles, and The Wilds - we don't mark them on the map - but one's more ancient civilization, one's more Maldivian white sands, one's more dark and oppressive. I'm sure beyond launch we're going to expand the size of the map, as we grow. We'll look at increasing ship numbers per world."
Neate continued explaining that Rare already has some ideas in store for after launch: "We've got a lot more island designs waiting in the wings... and we've been considering when to build and add those in."