The coffers are full, the playing stocks are almost at miraculous levels, the All Blacks are seemingly entrenched in that world number one spot and it feels like it would take something unexpectedly colossal to derail New Zealand rugby.

And it doesn't look like there any icebergs in the immediate vicinity. The All Blacks would survive losing the series to the Lions and no great damage would be done if they drop a few other tests this year.

Having only lost four tests in the last five seasons, their reputation would be dented but hardly ruined if 2017 sees them post an 80 per cent win record rather than 92 per cent as they have done since 2012.

Clearly they would rather avoid testing that theory and without burdening them with excessive expectation, it's hard to imagine them doing anything other than maintaining their relentless excellence.

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But there is, however, an iceberg on the horizon. Barely visible but nonetheless there is something lurking in New Zealand rugby's future that is going to potentially have a massive bearing on the All Blacks' fate once they reach 2020.

Current head coach Steve Hansen has told the Herald he almost certainly won't be staying beyond the World Cup. And when he retires the New Zealand Rugby Union will have to make a huge decision on who replaces him.

It's huge because as Hansen said: "It comes down to do they [NZR] want continuity from a head coaching point of view or do they want someone new. That will be up to the appointment panel. There are some good candidates."

Hansen, having been re-appointed as an assistant to Graham Henry in 2008 and then promoted to the top job in 2012, is a confirmed believer in continuity.

He is living proof that patience pays off and that international coaches need time to learn the craft and that often the best place to do that, is from inside the camp in an assistant role.

While he has to promote such an argument given that it was his route to where he is, the statistics make a more compelling case. Since 2010, the All Blacks made the jump from good to great.

That year they only lost one test. In 2011 they won the World Cup and in the subsequent five years, they have only lost four times.

The record is phenomenal and the last seven years have been the best in the professional age, if not the best period in All Blacks history.

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The decision to reappoint Henry and then promote Hansen - to support a continuity policy - has been arguably the best strategical move the New Zealand Rugby Union has made in the last decade.

Henry's survival after the disastrous 2007 World Cup campaign was initially hugely unpopular, but could anyone now, hand on heart say it wasn't the making of this golden age of excellence?

If Henry had been ditched in 2007 so too would Hansen and the All Blacks would have been back to zero in terms of institutional knowledge held within the coaching team.

Instead the coaching team used their mistakes as their guide. Instead, the coaching team had practical experience and knowledge that enabled them to select better and to coach more strategically and compassionately.

Having seen how a promote-from-within policy can be so successful, NZR will feel a strong temptation to appoint current assistant Ian Foster to the top job in 2020 should he apply.

Foster's case would already be made - continuity has worked before and it can work again he will say.

There would be no argument with that and NZR chief executive Steve Tew acknowledged as much this week when he said Foster was probably in pole position to succeed Hansen.

But equally, NZR would have to be wary that they aren't shutting the All Blacks off to new ideas, to outside influences. Another continuity appointment could easily endorse a culture of complacency and potentially arrogance.

What will also prevent any rubber-stamping of an inside appointment is the probable wealth of external candidates.

With Hansen having flagged his intentions early a few good New Zealand coaches may decide to free themselves up to have a crack at the job after the 2019 World Cup.

Potentially Joe Schmidt could finish up with Ireland at the World Cup and put his hat on the ring for the All Blacks job. Warren Gatland says he's coming home as well in 2019 and Vern Cotter, who challenged Hansen in 2011, now has international experience with Scotland.

The likes of Dave Rennie, Todd Blackadder and Jamie Joseph may be interested, as possibly would Chris Boyd and John Plumtree and the All Blacks, it could be argued, may be ready by then for a different way of doing things.

An external appointment would come with some risks. A coach with significant offshore experience may impose ideas and values that are alien to New Zealand rugby culture. As Gatland is discovering in his current role with the Lions, what works in the North doesn't necessarily translate that well in the South.

But an external appointment would also have an element of excitement and if nothing else, it would show elite New Zealand coaches that there are multiple pathways to the All Blacks job.