Except Jolly Roger pretty much is already in the game as a boss: Invading Islands.
Davy Jones, would love to see at Tormenta(Autograph and Camera in hand
) But he can only set foot on land once every ten years.
Beckett? Not much to say really..
But even if they were bosses, im sure that they would save them for something kinda like the Black Pearl boss battle and not one of the respawning bosses like Whit Widowmaker or Remington. Would be cool though!