Would there ever be any pressure from the A-League itself to build a football-purposed stadium, especially given how obvious the success of soccer-specific stadiums in the MLS is? I might be getting my facts mixed up but wasn't Western United given a license on the condition that they would build their own stadium?
I think you are right re WU. But they were a new team in a city already with 2 teams. I think the idea of a new shiny stadium out in Western Melbourne, was to help the team carve out it's own supporter base & identity. Plus everyone loves visiting a shiny new edifice the first few years. Remember the Super Rugby crowds at the ROF first few years after it was built.
I think the APL would just be ecstatic to get a $10M plus licence fee off the new Auckland & Canberra owners without budening them with extra costs.