The 10% of the market who could afford in that scenario are pretty much the ones who have been driving it up in the first place. They have disproportionately expansive wealth compared to the rest. I agree it will slow down eventually, but for other variables, like a downtrend in foreign investment. I think majority market affordability will have little to do with it, without government intervention.
Also the more Melbourne sprawls, the more inner suburban properties will push up by virtue of comparison. I think it's gonna take a recession or a serious drop off in the rentals market to stop this train.