The fact that there are lots of people in India or Indonesia does not matter. I feel that of the billions of people that live in India, only a small fraction could afford a Disney vacation. However, Australia is a wealthier country with a greater fraction of people that would visit a Disney park. Also, if a resort is unique, people from the entire world will come. Even if someone lives in Orlando or Los Angeles, they may still travel to a foreign park if it provides something different enough from what the states can offer. I do understand that many people live in East Asia, but, not all of them go to a Disney park. Hong Kong is in a highly populated area (and easily accessible to other highly populated areas) yet it is one of Disney's least attended parks. This why I would still strongly push for an Australia park. Once again, I can't wait to hear your ideas because everyone has such a unique way of making their own theme parks.
You are correct that "only a small fraction could afford a Disney vacation"-- the middle- and upper-class population of India is only about 4% of its total population. However, that equates to over 267 million people, almost 12 times that of Australia's entire population. Indonesia has over 100 million middle- and upper-class citizens, and the ASEAN region has a growing middle class. There are more middle-class and affluent people in the region around Singapore than there are in Australia. Australia is more remote, less centralized, and less populated. All in all, more wealthy people would have access to a Singapore park than an Australia park.
Singapore is a very English-friendly country (it is one of the official languages) and is a world leader in commerce. I believe that, in real life, an Australian park is simply not sustainable. You mentioned that international travelers may come to an Australia park. Why would an international traveler not visit a Singapore park? Moreover, Tokyo Disneyland receives very little international travel, and is still extremely popular because of its great demand. And speaking of demand, more international visitors to Disney parks are from Asian countries than any other region, despite two (soon to be three) parks in the region. Australians are less likely to visit foreign parks now, so why would they visit a domestic park?
A similar example is the failure of Disneyland Paris initially: one of the many factors that led to its financial woes was a lack of interest in the park. In Tokyo, Japanese tourists had been visiting Disneyland consistently, and in large numbers, for many years. Europeans, however, had less interest in a Disney vacation. Therefore, Tokyo prospered, while Paris floundered. More Southeast Asians visit foreign parks than Australians.
I'm sorry if I sound aggressive, and, remember its your park, and this isn't real life, so it doesn't have to be realistic. I just wanted to put in my opinion. Good luck with your park!