Not quite sure what you are on about with regard to DUD and the runway length.
Freedom Air was operating B733 DUD to Aussie they are still doing the same with the Bus so there is obviously not a problem with length at DUD for Trans Tasman operations.
The original runway was built for B737-200 Basic operations, complete with approach RADAR services. NAC even built a hangar for the overnight B737 to be housed. The runway was lengthened in the late 1980 to allow direct Tasman operations by B767-200 aircraft. I believe QF have operated a 200 there last decade on a charter basis however there is not the population base to support an aircraft the size of a B767.
Yeah have to agree there seem to be no problems with the airbus or B733 and the current runway length (1960 x 46 - PCN 60) The airport company already own all the land at the south and west of the end of the runway and I believe its already designated as runway and the plans are there for another 500 metres but why spend the money until the need arises when until then it can be put to better use.