I’m fairly ambivalent on the idea of joint currency with Australia, but UMR has found support for it up from 29% in 2000 to 49% today.
Dr Cullen, and some others, are adamant that the only way Australia would agree to currency union is for NZ to adopt the Australian dollar.
I think he forgets politics is about deals. In the right circumstances I believe one could get Australia to agree to a new currency with a joint Reserve Bank. It might be after we have won at the WTO over apple access (not saying we would necessarily want to make that trade), or when there is something else to negotiate, with.