This post doesn't make a lot of sense. Where are you getting 4c/pt value on Y redemptions?If only Marriott would partner to open a credit card in Australia.....
Additionally, Marriott points are generally worth 0.8c/pt and most Marriott cards earn, at most, 4x on non-Marriott spend, meaning they earn, at most, 3.2c/point.
And the earn rates would be worse in Australia due to lower interchange fees.
In other words, even your wish is unrealistic.