It's been dubbed the biggest tax shake-up in a generation. But it's all talk. There's no chance it's going to happen. At least not to the full extent the Tax Working Group is recommending.

Some of the shake-up will happen. Maybe enough to qualify as a low-level tremor. Maybe it will include capital gains taxes, maybe it won't. Yup, maybe none at all.

It's all too early to say. And that's for three reasons: Winston Peters, us and Labour's own self-interest.

Let's start with Peters. The New Zealand First leader has publicly opposed a capital gains tax as recently as the 2017 election campaign. "Off the table" is what he said.

He's got good reason to oppose it. He's trying his damnedest to win over provincial New Zealand and a capital gains tax could hit them hard. Which farmer selling a big farm would be happy to hand over a third of the property's capital gain to the Government?

It'll be hard for Labour to get anything across the line without Peters given he's the coalition partner. Which makes him Labour's get-out-of-jail card, but I'll come back to that.

The second reason this exact tax package won't eventuate is us. You and I. Capital gains taxes are not popular. In a poll this week, 54 per cent didn't want a CGT, 32 per cent did and 14 per cent didn't know.

That was before the report came out. So those Kiwis were thinking about a hypothetical tax. Essentially, it was a question about their principles. Talk to them now that they know the proposed tax would take as much as 33 per cent from their house's value-up and they might answer differently.

Of course, they could be convinced by a corresponding drop in income tax rates. But is $16 a week enough to convince you to hand over 33 per cent of your valuation increase?

And then there's the question of whether the Labour party itself really wants to implement a capital gains tax. I know they say they want to, but do they really want to?

Labour knows how the public reacts to more taxes. Remember, during the 2017 election campaign, when Jacinda Ardern made the captain's call to bring in a capital gains tax ASAP? Labour's polls starting dropping immediately. She was forced to recall the captain's call to save the campaign.

Once bitten, twice shy maybe.

Perhaps that's why Labour is already talking down the chance of a CGT. Finance Minister Grant Robertson is already saying it's "highly unlikely" all proposals would be implemented.

So, most of us don't want capital gains taxes, Peters (last we heard) doesn't want them, and Labour may not really want to lose an election for them.

Why do it? Credibility is why.

A CGT was a Labour election promise. It's all about making the tax system fairer. It's a Government looking after the poorest Kiwis. Robertson and Ardern have both spent too much time repeating that message to now walk away from their one chance to fix the system.

This is where Peters comes in. If he continues to oppose a capital gains tax, he might be their get-out-of-jail card. They might be able to happily drop a CGT and blame it on him. They could trot out the old you-win-some-you-lose-some argument. They've used it before.

It's of course true that coalition governments require compromise.

But will the Peters excuse be good enough? Ardern and Robertson will have to use all their charm and communications skills to sell that message.

Either this will be the biggest tax shake-up of a generation, or the most convincing PR campaign to explain why it never happened.