I'm not a fan of referenda in general. But John Key's painted himself into a corner on this one, having promised that he'd never touch superannuation. Everybody knows that best policy here is to announce, today, changes that will start phasing in at some future date. For example, the government could today announce changes that would apply from, say 2022, when the age of eligibility would then start rising by a year every 2 years or so, and that, from 2022, Super would be CPI-indexed rather than wage indexed.
Rob Hosking says the challenge makes Key look gutless; ultimately, he's likely right.
This could have provided a clean way out for Key. Having promised no changes, Key could have announced a referendum and say that he wouldn't reverse his promise on it unless he had a specific mandate.
Except the immediate move from Labour would be to frame it as a win for Labour. And Key won't want to hand them that.
The only way it works now is as a referendum on a bundle of changes sufficiently different from whatever Labour's proposed that Labour can't claim it as a win. Either that or getting a time machine and running the referendum before Labour moved to support changes to Super.