noroad:
Personally I think that marketing the New York to Auckland leg as a "Direct", instead of "Non - Stop", and planning for a fuel stop in say Tahiti is an option worth considering. Would mean that Air NZ could sell the entire plane, carry fright etc. And on flights with low loading's, the stop could be skipped.
Or, they can just buy the A350ULR (or 777-8 if it ever arrives) like Qantas and job done. As great as the 787 is, its not a perfect fit for the ULR question.
Most of the smart money is betting that the B777-8 will never show up as a passenger aircraft: there are only a few dozen on order and the earliest they could be delivered is probably 2026, maybe even 2027. The B777-9 is sliding into 2024, and Boeing intend to build and certificate the B777-8F before they start work on the B777-8 passenger aircraft.
The B777-8F is not just a freighter version of the passenger -8, it's actually a bit longer - maybe a "B777-8½F" 😂. I guess Boeing could re-announce the -8 based on the -8F fuselage, but that would make it heavier and shorter-ranged than the originally announced -8 and even harder to market.
Air NZ's problem is that it is planning to have only a single aircraft type in each of its jet fleets - A32x short haul and B787-x long haul, and it would be there in only a couple of years once the last of the B787-10s arrive and the B777-300ERs are retired.
Going back to having two rather different types (B787 & A350) on the long haul fleet would be a step backward for their labour cost & flight crew flexibility.