Can the A380 operate in and out of places such as Perth, Brisbane or Adelaide?
Yes.
Or does this spell the end of Qantas operating internationally from anywhere but Sydney and Melbourne?
Yes.
To be honest I'm surprised they even suggested Qantas, as an aircraft operator, will exist by 2021. I suspect they have few plans for Qantas to be other than the umbrella organisation (to comply with the Qantas Sale Act) for a series of offshoots, perhaps even as early as 2015-16.
One part of former Asian culture they appear to have adopted accurately. There'll be no 'loss of face' that would be displayed in backing away from a concept that appeared flawed from the outset. (And obviously no subordinate 'crew member' willing to tell them they are making an error. It won't matter. They're not listening.)