There've already done crazy things like replace the Motorail with an XPT and close the Murwillumbah line.
The Sydney to Brisbane XPT always had the advantage for me of being an overnight service.
Changing the schedule as Trainlink proposes would also render the XPT useless as an overnight train to the Tweed and Gold Coast areas. It would also make ongoing connections to the Sunshine Coast, Ipswich and Brisbane suburban areas both by train, bus and ferry difficult if not impossible. It would also stop passengers from being able to see the scenery round the border loop area.
So they can't completely stop passengers using the train, they need to make it unpopular.
Wouldn't swapping the Brisbane and Casino XPT schedules around with a few adjustments be a better solution than having odd arrival and departure times?