Just to add my 2 cents here (yeah, I know, six months too late!)...
There are various public statements out there which say that using an SWR of X% that would apply for the usual 30 years period is more or less equivalent to planning for eternity. Well, I don't believe this is quite true. I want to early-retire, I don't want to bet on a premature death (who knows where medicine will bring us 20/30/40 years from now), so my projections are usually 45 years - and I am 51, and I suspect many of you guys are younger. In other words, a 50 years time period isn't that crazy.
Then I did a ton of backtesting with my own Excel sheet, using various asset allocations, various withdrawal methods, various assumptions on returns, etc. And I ended up noticing that a 40 or 50 years time period is actually significantly harder to satisfy, as there are more sequences of stock crisis which end up destroying your portfolio, the effect of the first few crisis being tolerable over 30 years, but one more crisis later on can be the final killer.
In the US (I insist, since the OP is in Australia), backtesting over 40+ years with a 4% WR can turn out to be problematic. And then you can indeed speculate that the rosy picture of US returns in the past 100 years may not repeated in the next century, notably with 50 years ahead of you. And then you have to customize per country (yes, Australia also had a fantastic run in the past century, but well, same thing, will that last?).
The probability of 'black swan' events (something really big, really damaging, and hard to predict) also gets significantly higher.
So, I don't know, but I wouldn't want to bet on a 4% number (in the US or Australia) for such long time period. But hey, as the other folks pointed out, all is not lost, if you have such long time period, well, you'll find plenty of opportunities to make some additional income through activities that you truly enjoy. So maybe a rule of thumb could be to use a 3% rule on your accumulated portfolio, use a proper variable withdrawal method (e.g. Guyton-Klinger or Hebeler) to make it better navigate the vagaries of the market, AND plan for some reasonable side-income to fill the gaps.
It is amazing to see how side-income in the early years, plus some form of pension/SS in the later years can make the overall equation look much better... That was my big discovery a few months ago when I was at the height of playing with such number crunching...