New Zealanders will be able to patronize their own tourist industry, as a start. Then there is talk of allowing travel between Australia and New Zealand, because Australia also has low case numbers. Other countries also are getting to low case numbers, so those could also be added to the list in time.

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.