Back of the clock?
My speculative guess is that the A320/321 could be used for back of the clock international flights such as from Darwin to SE Asia and more so from Sydney/Melb/Bris to South Pacific.
In NZ there are a lot of overnight flights to Cooks, Fiji and Samoa from Auckland by Air NZ and DJ. Should keep aircraft utilisation rates high as you can do domestic during day time and an international overnight which avoids Sydney's curfew restrictions.