What about Pokemon Spring Version and Pokemon Winter Version. Although Australia is a hot summer place, it's dream world variant on the other hand could be something else entirely, deserts turned into lush flower fields for Spring version and into icy cold snowy landscapes in the Winter Version.
Again, we kind of already had the seasons theme in Unova, though a Summer and Winter Version could be cool. Like how you can travel between Alola in different versions in Sun and Moon, you can visit the Winter world from the Summer world and vice versa via a portal.
Ever since that fake Platypus starter was going around a few months ago a region based on Australia sounds like it could be very cool! Besides that I always loved the anime arc when Ash and friends went to the Orange Islands, so that could be fun - but it might be alittle to similar to the Alola islands. I’d also love a tropical/rainforest region based on the Amazon. The local “gang” could be indigenous tribes
The annoying first-route Pokémon could be a dingo, a wild dog that is widespread around Australia and is seen by some as a nuisance. It could be a Dark/Normal type. The regional bird could be a kookaburra or a budgie, and it could be Fairy/Flying to counter the dingo’s Dark type. After seeing the Disney movie
Moana, I thought the legendaries could be based on the volcano and earth deities, with one geared towards destruction (Fire/Rock or Fire/Ground) and the other geared more towards construction (Grass/Fairy), though I think
Moana is set in New Zealand and not Australia, and it would be a bit too much like Alola anyway.
Remember how I said Canada could be cool as a region? People like to joke that it’d be basically like Snowpoint City in Sinnoh with permanent snow and ice, but Canada does have some variety in its landscapes and geography. Someone even made a thread on this forum many years ago that Sinnoh was based on Canada, although it mostly takes inspiration from Hokkaido in Japan. I made this collage of the different states/provinces around Canada so you can see the diversity of its landscapes: