The whole situation is not easy even for U.S. tax experts to consider.

Here is the double tax penalty:  No credit or consideration of Australian tax on Superannuation.  So both Australian and U.S. tax would apply with no credits. Double tax = more tax than Australian only pays, everyone resident in Australia.

Even in the situation of credits, the U.S. is not justified in claiming tax jurisdiction over Australia.  This is similar in concept to you were born & live in New York. Now you move to California and become a tax resident there.  Is it right and just for New York to insist upon a double state tax claim on you, you no longer live in New York or may receive resident services and benefit of New York resident infrastructure.

The credits are siloed as well.  Australian earned income tax goes up way higher and sooner than U.S. income tax.  So there is an excess of tax paid over U.S. earned income tax.  Yet one is not allowed to apply the excess to U.S. tax on Superannuation.