Currently the terminal structure of T1 and the connections is not fit for purpose. PAC have no plans to remedy that in the short or medium term.
I guess that depends on your definition of 'medium term'. I understand PAC is desperate to get moving on the new pier at the eastern end of T1, to be followed by the development of a new terminal for QF next to T1. Their 'plan' is to have that completed by 2025. I suspect that PAC believes their business case for making that happen will be undermined if they allow QF to keep pushing their international services across to T3/T4. That would then slow down PAC's plans to consolidate all the terminals within the Central Precinct.
When is an underground airport train station, not an airport train station? When its built at just under 1 Km from the nearest terminal...T3 / T4.
In the short term perhaps, but Redcliffe Station is intended to serve the wider Redcliffe area, not just T3/T4. Why build a train station
at T3/T4 when the plan is to move everything over to the Central Precinct within the next ten years? The Airport Central Station is located in the heart of the Central Precinct and will serve all the terminals once everything is consolidated on that side of the airport.