With all these international $$$ rolling into the market it's hard to see it stopping very soon or very suddenly. Especially in Sydney (which gets much more international attention than any other AU capital city). I think unless there is some regulatory measures (similar to Hong Kong's 15 per cent surcharge on non-residents buying into their real estate market) we won't see a sudden hard crash of valuations.
The danger is that Sydney can become a version of Vancouver where no middle class family can afford to buy a property since the market is heavily dominated by unregulated foreign investments and heavily inflated prices. Vancouver has become one of the most unaffordable real estate markets in the world due to a surge of international immigration and offshore investing. The only people who can afford to purchase housing in Vancouver are extremely wealthy, usually from offshore and often able to buy in cash. So good luck to the local middle class in competing with that.
That sounds like good news for people who have already bought