Interesting this discussion kicked off over the capacity of the new Perth Stadium. I know the AFL are greedy but whatever your bows on the GF moving from the MCG one day, I believe it's a separate discussion to stadium capacity.
Some of the largest soccer games in the world have been played at sub 80k stadiums including World Cup and Champions League finals. The WC final, a global event only played once every four years, played at stadiums holding in some cases well under the 80k mark. The MCG is one of the largest stadiums in the world (and mostly has college gridiron stadiums for company), so while it is filled for GF's, using that as the 'minimum benchmark' for how large a GF suitable stadium should be is like using a Ferrari as the benchmark for how quick all road going cars should accelerate.
FIFA happily saw south africa build a stadium in the bush wasting scarce goverment resources (don even mention qatar) so hardly a model to be following Soccer crowds are 80% adult males so that would be completely alien to our sport
Easier for the naysayers to change to soccer, see how much FIFA cares for you in Perth and Adelaide. Success is totally secured by the big countries and clubs