The trigger could be a slowdown in resource industry. That may in turn lead lead to:
-> lower government revenues -> cuts in subsidies and tax breaks related to housing and banks -> broader cuts to government spending and higher taxes -> higher unemployment -> higher bank lending standards -> domestic pressure to reduce immigration intake and less demand from migrants ->lower AUD -> higher foreign debt servicing -> reduced bank funding availability and higher costs
There are lots of nasty negative feedback loops as we saw in the GFC. Its a bit early to be calling all this yet imo but no reason for complacency. We've dodged one bullet and seem to be getting a little over-confident. The government is not so well positioned to come to the rescue if there was a second aftershock.