maybe not in the next few years, but i reckon in my lifetime China will emerge to be the worlds superpower, they have the population, their economy is continually growing they just arent doing a thing wrong. Noone is able to stop china either because of the vast mass of people over a huge area. They also have a stable government (whether you agree with the system at all - its stable)
India could be a superpower but they wont as long as they are battling pakistan for kashmir but the country is rapidly developing and like china, they have the population on their side.
Japan is limited by space more than any other country, they are already packed now and they are stsrting to have problems with health - the country has been disinfected for so long that they are a starting to get super bugs that are immune to known cures....
Australia on the other hand has more room to expand than nearly any other country, we are just about built on a sea of uranium and have a stable government, great economy (thanks keating!) decent education system and such, all we need is the population