Years ago I used to spend time in NZ when I was part of the US Antarctic program which stages out of Christchurch. In the late 90's when I was going down there, one of the airlines had my favorite promotion ever: for NZ$99 (about USD$59) they would give you a round trip ticket to somewhere. You'd find out where you were going after you bought the ticket, and they'd guarantee it was a same day round trip. I always thought what an incredibly fun and cheap way to spend the day in a beautiful country.
"For me, the biggest question is whether visitors will be able to get travel / health insurance to cover them in New Zealand."
Or the NZ healthcare system could just cover visitors with the understanding that the benefit outweighs the cost?
Maybe even tourists "from anywhere" could be allowed to visit if they just agree to isolate upon entry for N days first. Private hotels and resorts could offer isolation packages. For many tourists, travelling to New Zealand is already expensive so they usually come for longer because it's a once-in-a-lifetime trip... adding N days of isolation to the start of the trip might not be so bad, especially if there are good deals to be had.
For me, the biggest question is whether visitors will be able to get travel / health insurance to cover them in New Zealand. I suppose the New Zealand government could sell such insurance, or they could back a private insurer.