I mean, yes - and no.
It does seem counterintuitive to build in Adelaide when Sydney, Melbourne and even Brisbane are more populated centres - but Adelaide does have one thing going for it - space.
There are large tracts of agricultural land less than 30 minutes from the Adelaide airport (if you head north of Salisbury for instance), and the city is in the middle of that path - so potentially 15 minutes to your hotel and another 15 minutes travel to the park... Disneyland was an orange grove when it was first built and the population sprang up around it.
Neither of the three east coast capitals could offer that proximity.
Not sure about a hotel, but there are very loud whispers within the cruise industry at the moment that DCL is bringing the Wonder Down Under (Just thought of that... that's a great marketing slogan right there too!).
All of DCL's ships have had their schedule released for next year, except the Wonder which has been blanked from September 2023 onwards. The Magic has also taken over the Wonder's previous schedules out of Galveston and New Orleans, and I believe the Wonder is doing the Summer in Alaska which puts them in the Pacific priming them for a trip to the South Pacific. Disney has also registered a company in Australia "Magical Cruise Company" last October, and in April this year they registered the Disney Cruise Line trading name. Further, there are current port 'berthing' reservations for an "Unknown" cruise ship flagged under "Unknown" Cruise line.
While unusual, this isn't proof that Disney is coming, however it's unlikely there are two unknown ships, from an unknown line, berthing at two different terminals in Sydney 30 minutes from each other so it's likely arriving at White Bay after the trans-pacific crossing due to potential customs and quarantine issues, and then transferring to the OPT for overnight turnaround and media previews before welcoming it's first sailing from Oz.
*Can't take credit for most of this info as it was gathered together by others. Try googling "Is Disney Cruise Line coming to Australia".