When I was at the media brief on Wonder's inaugural, they were asked would an oasis class ship ever be built for the APAC region, and responded with something along the lines of "we have many Oasis class ships and would love to try and bring one to that part of the world when we can".
Technically, Japan and China doesn't have to be open for Wonder to come. Australia market could serve half the season, with another half from Singapore. In this scenario Spectrum would be surplus ship and they wouldn't know what to do with it. They could send her to BNE/MEL/SYD and rotate between Singapore and Australia both ships.
That would be nice, having both Singapore and say Brisbane with Wonder half of the year each and then the rest of the year Spectrum in between Singapore and Brisbane. On top of say Quantum from Sydney.