I'm not knocking NZ because their armed forces contribution to operations surpasses many larger nations but there is no guarantee that New Zealand will purchase P8s or equivalent:
NZ was going to lease 28 x F16s - cancelled
The "Huey" replacement was to be 10 to 12 airframes - 8 ordered
They had options on 8 x C130J - 5 x C130Hs upgraded
The Navy wanted 3 x ANZACs - 2 entered service
etc etc
I hope I'm wrong in reality NZ will be lucky to get SC130J or even an aircraft such as CN295MPA
Other, kiwi members of DT could provide better information, but there does seem to have been an element within Gov't which has realized that the NZDF has been cut back, with capabilities having been lost due to a lack of proper funding, to the point where the force could break under the right (or perhaps wrong) conditions. Perhaps more importantly, the public perception has begun to change.
Under prior Gov'ts the NZDF funding was slashed, and it seems that this was done deliberately to limit/weaken the NZDF, as well as increase the diplomatic distance between NZDF and friendly nations like the US.
There were also steps taken were money was IMO wasted, because the "cheaper" options were taken. The C-130H SLEP is a prime example. $50 mil. per aircraft was spent to upgrade, modernize and extend the life of aircraft which had served the RNZAF for approx. four decades. For approx. $15 mil. more per aircraft, new C-130J aircraft could have been purchased which could potentially serve another forty years... Who ever signed off on the upgrade vs. replacement either never looked at the long term VfM, or did not care.
At this point NZ is regaining access and trust with other, key partners. In order for that to be maintained, never mind improving the relationship, then interoperability is needed. In order for this to be accomplished, at least some examples of advanced kit like the P-8 Poseidon are needed. Not necessarily a 1:1 ratio, but certainly three or four in order for the NZDF to maintain a limited deployment with friendly forces.
-Cheers