I've hinted on this in a past post. PD has to get some Australian venues included (even if fictional street courses). PD went through some of the trouble getting in Korean makes and adding the love-it-or-hate-it Seoul street course. It would be asking too much, but I think every nationality of car featured in GT1 should have at least one track so you can have a semblance of home pride. Think of how there were a lot of American cars in GT2 with a few venues to go racing at in America (Seattle and Laguna Seca). You have a sense of home pride racing cars from a certain nationality of car. Australian cars have been in GT since GT3. However, never any real home field advantage. Bathurst would obviously be the best fit. However, places like Surfer's Paradise, Adelaide, Sandown, Eastern Creek, Phillip Island, and Queensland are great venues to look into if Bathurst isn't available. MAYBE even Albert Park wouldn't be bad to look into (even though Codemasters has the F1 licensing).
I've been educated about Australian racing since 2000 or 2001. I love the roar of those Australian V8 Supercars and just how intense the racing action is. That's not to mention the Holden vs. Ford Australia rivalry. I even valued being introduced to the late great Peter Brock. While I've been proud to be able to get myself the Tickford supercars in GT3 and GT4, I'd love to see Holden V8 Supercars just to make the Holden/Ford Australia rivalry relevant in GT5. Imagine an online battle with 12 or 16 or so people racing either Holdens or Australian Fords. Polyphony Digital planted the seeds of showing off Aussie muscle in Gran Turismo. Now, they need to turn that little plant into a branching bold tree of Australian racing goodness. I'm speaking with passion on the notion of Australian cars because I love exploring the automotive and racing worlds. Australia would include that fourth different continent of motorsports goodness Gran Turismo fans would love to have. It was still fun racing that FPV in one of the GT4 License Tests at Apricot Hill. So at least these cars are being utilized in a way and not just left for dead like in GT2.
I'd be more than happy to see Australian presence in GT5. Just enough to make Australian fans happy while other car enthusiasts the world over can be more than happy to race Australian cars and Australian venues.