The whole premise seems flawed though. People don;t have to just hop off early from their Adelaide booking - QR will sell MEL-DOH-LHR and v/v on the flight anyway. There is seemingly demand for ADL-DOH services since QR also runs a non stop service on that route too

Whether QR was only granted access based on also serving a lesser destination with the service, I don;t know

Also, this hopping off early only really works for passengers that have a one way ticket to Adelaide - those buying a r/t to Adelaide would find their inbound cancelled due to the no show and those trying to hop on in Melbourne with an Adelaide ticket would not be allowed through to board