I know the messages in favour of regional Tasman flying (like Hamilton, Dunedin, Rotorua, etc) are old, but it's still important to note that regional airports in NZ have traditionally not been able to support Tasman routes. The demand just isn't there.
The notable exception is Queenstown, but its close to ski fields and is a major tourist trap. Rotorua is somewhat similar. However there is very little to attract people to Hamilton and Palmy, and not all that much at Christchurch. And that's before the ridiculou suggestions of Taupo and other small centres.
Air NZ knows this - so they're not going to do it. They tried (not particularly hard) to make it work at HLZ and PMR and they've lost their flights. I think DUD is losing some/most of their's and I see no reason why they won't lose the rest. It really is use it or lose it, and unfortunately, people don't use them.
Rotorua and Queenstown are the only regional ports that have a decent business case. I might be biased as I'm from Rotorua, and they're already pouring money into work for our non-existent international flights, but that's still my opinion.
Tiger is not going to change this, as much as I would love to see them try.