That's true, they'd need a hell of a lot of content to make an entire continent the basis of a Pokemon game.A region based off of "Australia" would not be very good. it's a continent almost the size of Europe, and regions are the size of "the Northern Half of France" or "The Hawaiian Islands".
I'd rather see a region based of one of the states of Australia, like Queensland (not at all biased here). The whole country is just too big for a single region. And New Zealand wouldn't be "post game content" to Australia, if anything, it would need to be it's own region.