Gothic themes never get old. A Haunted World seems like a very strong candidate for a new Mario World. Perhaps that is where all the ghosts live, and they began setting up houses on other worlds.You could have the Haunted Ship and other Haunted Themes. The world has strong visual themes, great potential for interesting new enemies, and the level design would be varied. Entire games can sell on the haunted theme so a Haunted World would work.
How about The Flying Dutchman as the final level in such a world? Of course, in the Mario game the ship would ACTUALLY BE FLYING. :)