Edit: IANAtaxL but NZ does have a pretty sweet deal where new residents get to not pay tax on overseas income for four years. So Urs could come in for four years. Then if he maintains a permanent home in the US that is always available to him (not rented) a tax expert might argue he is dual resident and under the dual tax agreement would tie break to the US so doesn’t owe tax in NZ on his US income, which would be all of his income. So this is probably what he would do. It’s a pretty sweet deal, I don’t think it’s fair you basically don’t pay tax to NZ under that arrangement if your income is overseas and you can afford to leave a house unrented.
Wouldn't you still pay US tax as a green card holder or citizen? After decades in the US would be surprising if he wasnt.
(And even if not, does the US have an exit tax when giving back green card or passport?)
NZ also has universal healthcare. For anybody tired of the US healthcare "system" (what we have doesn't deserve to be called a system), that's very attractive even if you're not wealthy. Especially not if you're wealthy.