Virgin has become quite comfortable using its Perth -700s across many east coast routes, so QF will be no different.
A220 would do triangle off peak no doubt.
One would expect OOL, CNS, ADL, TSV will all be popular spots for the thing. The question is how far can they push the A220 around the network. Wouldn’t surprise me if 2xA220 flights are cheaper vs one mainline flight. Thats the subsidiary playbook in action.