With the cost of a new ship in the area of a billion (yes, billion with a b) dollars, Disney isn't likely to expand the fleet anytime soon with Avitar land just breaking ground and a just promised expansion of the Star Wars franchise in the parks. While I would love to see new ships, Disney is filling their ships (this is the 1st time in years that all of the September cruises haven't had FL resident rates) so they don't have to discount them to fill the ships. There have been some slips in new destinations (Galveston and NY were a bad financial move as many cruises were discounted) becoming more permanent home ports so
DCL is concentrating where they make money - Florida, & Alaska with some side trips. That being said, I do agree that if they sent a ship to Japan, they would fill it year round and wouldn't be completely surprised if that was a "test" destination in the near future for the Wonder.