I'm expecting an average payout of around 25% per annum over the...

I'm expecting an average payout of around 25% per annum over the next 2 years.
My AXI holding is only a tiny fraction of my portfolio. I would have loved to have held more, but it was extremely difficult to get set at the then prevailing prices.
I wouldn't worry one little bit about Aussie house prices as they relate to Axiom's development pipeline.
Their Glenlea estate has so much going for it. It is a multi-year, multi-stage development wherein allotments have been selling comfortably ahead of schedule at prices higher than originally predicted, thanks to the sustained boom in housing.
Also remember that Mt. Barker is THE boom growth region of Adelaide; prices are relatively affordable; and Adelaide now leads the other capital cities in house price growth, at a time when the two major capitals are flatenning or softening for the reasons you outlined.
Axiom cleverly offloaded some of their risk by selling roughly 20% of the estate last year to another entity. Also remember the nature of broadacre development: the developer is only committed to producing lots one stage at a time in line with short -term projected demand, unlike a commercial property, say, where you could be caught out by the cycle with only 60% precommitment.
My general feeling is that Aussie house prices will fall harder this cycle than it has for many decades, but that Adelaide will weaken only half as much as Sydney and Melbourne. I wouldn't be buying a house now to invest, unless it had some strategic value.