I'd leave the Southern Cross in - it has always represented the Australian land mass. It's not politically loaded.
On the other hand, the Commonwealth Star represents the original 6 colonies and "The Territory of Papua and any futre territories" and needs to fuck off. Replaceit with something that represents a forward-looking restoration of indigenous culture and synthesis of settler cultures; The aspiration to build something worthy out of the cultural destruction of colonialism.
And then obvs the Union Flag in the canton should be replaced with either a Hammer and Sickle or a Drop Bear riding a surplus US submarine.
IMO, any country on the business end of colonialism needs to bring the symbols of the indigenous peoples to the forefront if we're going to start redesigning flags.