I've been considering a story that either takes place in Australia or just expands on what happened to Australia after the Great War.
Here are a few of my thoughts:
Australia is a US ally, is relatively close to China, and would likely have been affected to some degree by the War. Having said that, it could be interesting to consider that Australia may not have been affected that badly and may still have some sort of functioning society
Australia has massive amounts of natural resources, especially uranium (would be interesting to see how this plays into the Resource Wars)
Many interesting cultural landmarks that could be worked into the map, or even just the lore, such as the Harbour Bridge, Opera House and Centrepoint Tower in Sydney. Other interesting locations could be Uluru and Alice Springs (though this could be too desolate and empty to be interesting enough to explore). The Parkes Observatory (also known as "The Dish") may be an interesting location to work into the lore. Bearing in mind, Australia is an enourmous country, and many of these locations are in different states, many hundreds or even thousands of kilometers away from each other - I'm mentioning a few that could be part of the backstory rather than present in a playable worldspace (e.g. I doubt the Sydney Harbour Bridge and Uluru would be able to be in the same game outside of terminal entries and dialogue).
Australia is notorious for its dangerous wildlife and harsh conditions (outside of major cities of course). In present-day Australia, the Outback is filled with dangerous animals and creatures. Imagine an Outback affected by F.E.V. and radiation exposure (Legendary Glowing Platypus?)
Dunno if anyone else thinks this is a good idea or finds it interesting, I personally think its a great opportunity for a new DLC or mod.
P.s. before you say "Oh, but Australia would pretty much be Mad Max", just have a little imagination! I love Mad Max, but I feel there's a lot of potential for a Fallout interpretation of Australia to be even more interesting.