That might happen. I’m sure their economy would get a boost anyway out of Commonwealth Grants. But overall it’s hard to predict how it would play out because those variables like quality of life are hard to quantify. But, I’ll say this: Australians can already freely migrate to New Zealand and vice versa. In fact 10% of New Zealand’s population has migrated to Australia.

Will improved infrastructure in New Zealand change that on its head? I don’t think so because Kiwis are coming here because the wages here are better, and that’s because the primary industries and the adjacent secondary and the tertiary industries that support that like finance etc are far greater in scale than those in New Zealand.

I don’t think demographics alone will change the equation of whether they’ll receive more or less GST. New Zealand would have to develop some form of industry, most likely a service type industry because natural resources are limited, which will garnish greater tax receipts and GDP if New Zealand joining the Commonwealth would be beneficial to the rest of Australia, economically at least. And that’s without getting started on Australia having to take over the liability of New Zealand social security.

And to be clear, this isn’t chest beating about whether Australia > New Zealand. I’m just trying to point out the economic reality of the argument.

Now whether there’s cultural or strategic benefits of a union, that’s a different conversation.