Just to get rid of that annoying reminder about my lack of posts recently....
I have been reliably informed by those that know these things, that while Air NZ could indeed get earlier production slots for their 773s they will be paying full retail price rather than their contracted option price. For this reason it is still palatable to run the 744.
As for the 733 replacement, all plans are on hold. They know they won't last until 2020 when the NG replacement will be available, however nothing will do the job as well as the 733. So status quo for the time being.