Wouldn't hold my breath on this one. Skull and Bones was a huge flop, joke of a game, if you can call it that. The most beloved part of Black Flag was the ship combat and I doubt they'll perform better than Skull and Bones.
Among other entries in the series, Ubisoft is reportedly also working on the beloved Assassin's Creed IV: Black Flag Remake. The game is scheduled to follow Assassin's Creed Shadows in the latter half of the 2025. When AC Black Flag Remake does come out, however, fans can not only expect a graphical overhaul but also some gameplay additions.