It could work because they would sell it as a Qantas flight then put the customers on a JQ flight. Too late at the gate to do anything.
I was visiting the top end of Oz recently and a group of tourists were complaining about Qantas, many different reasons but the main one being they had paid for Qantas domestic flights and ended up on Jetstar flights. They were not happy and told everyone on our dinner table and surrounding areas.