I think Australia has missed the boat in terms of eradicating the virus like NZ. They were tantalizingly close, but now opening up with still community transfer in VIC (and to a much lesser extent, NSW).
The federal government seems to be pushing for the other states to open borders, and so closed borders and states within a NZ travel bubble are also not possible.
So, IMO, the travel bubble is unlikely now. NZ won't want to erase the hard work they've done.