I understand that the US currently has ADSB coverage down to about 1000 agl across 90% of the lower 48.
To save money AsA has less than 20% coverage at 1000 agl. More likely less than 10%.
In the US IFR aircraft remain in a minimum of class E airspace in all IFR approaches so ADSB gives a measurable advantage.
Not so in Australia- most small IFR aircraft fly in Class G and get no ATC separation service.
The US has no plans for an Australian type ADSB mandate for all IFR aircraft.