Whilst that sounds like a great idea, the big issue I see is demand for travel between AU and NZ is virtually non-existent and would be hardly enough to justify the added infrastructure needed to support such an operation. It's not just a matter of bringing NZ immigration officers over to AU to do pre-clearance but you need to segregate gates into three categories now, domestic, international and trans-tasman. To give you a sense of scale here: the number of daily flights operating between Toronto's Pearson airport in Canada and New York's airports is 28 for Chicago O'Hare airport it's 14, add another 4 daily flights to San Francisco and another 4 daily flights to Los Angeles and it's clear to see there is a ton of volume at Canadian airports to US destinations. Whilst I haven't counted the number of daily flights departing Toronto for US airports, I think the number is close to 100 if not more. Indeed the air travel market between Canada and the US is the
second largest in the world, not surprising considering Canada and the US share the world's longest border. Meanwhile looking at flights from Sydney over to Auckland, New Zealand's largest city it's just 10.
In terms of the story of this thread, which is the occurrence (with some regularity) of flights from Australia having to divert to AKL due to curfew, pre-clearing immigration wouldn't do much here. A diversion would still occur, and even if they are now land-side in AKL, would it have made much of a difference given they were unlikely to be provided a hotel?
-RooFlyer88