The unnamed ship dates in Sydney don't make any sense, though, unless Disney is planning a combination of short 4-night cruises and very long 16-night cruises from three different terminals in Sydney. If you find some unnamed ships in other ports that split those 16-night cruises into two 8-night cruises, then the dates become more believable.
It's very possible that Disney plans to enter the Australian market in 2023, but I wouldn't be at all surprised if they waited until 2024 when they have a 6th ship.