Should All Blacks coach Steve Hansen decide it's right to stay on, extending his contract to 2019 would be universally accepted as the right thing for New Zealand Rugby to do.

But it will also likely come with a negative consequence - it will accelerate the exodus of other aspiring test coaches offshore.

The number of good New Zealand coaches running other test teams is staggeringly high. Eight of the top-18 ranked nations are coached by New Zealanders and that will jump to nine when Jamie Joseph takes up his post with Japan after this year's Super Rugby. Also, Samoa are coached by Alama Ieremia, who grew up in New Zealand and played 30 tests for the All Blacks.

If there was a World Cup this year and the current top 20 qualified, that would mean 45 per cent of the teams would be coached by a Kiwi.

Advertisement

The concern is that by 2019, that number will have risen again.

If, and most likely when, Hansen signs up for another two years later this year, the All Blacks job won't be contested again until after the next World Cup.

That's a long time for aspiring candidates to wait and what many will be wary of is that the front-runner will most likely be current assistant coach Ian Foster.

He'd be no certainty to graduate, but will have obvious advantages: inside, working knowledge of the All Blacks, significant test experience and Hansen's endorsement.

"One thing I know is that Ian Foster has grown immensely as a rugby coach," Hansen said recently.

"He's always been a good man. He's learned a lot, as you do when you are at the coal face of an international team.

"The other thing I know is continuity is a good thing, and he would provide that.

"Whenever I leave, I think he's a really strong candidate, but there are a few other people who will put their hand up, too, and the Rugby Union will have to look at all of them. Fozzie is a very capable man and certainly capable of running the All Blacks."

Succession, as has proven the case with Hansen, has genuine merit. He was assistant for eight years under Graham Henry and yet still managed to have a significant and positive impact on the All Blacks when he became head coach in 2012.

To go down the same road with Foster is tempting. But the downside is it will deter other good coaches from staying in New Zealand.

For the likes of Chiefs coach Dave Rennie, the strongest All Blacks contender among the current Super Rugby coaches, the prospect of staying beyond 2017 may have limited appeal. If his aspiration is to coach the All Blacks, he'd have to determine how likely he'd be to win the job at the end of 2019 if he was applying without any international experience.

The last three All Blacks coaches - John Mitchell, Henry and Hansen - all had test experience to some degree before they were appointed. England, when they gave Stuart Lancaster the top job in 2012, learned the hard way it is a major risk to appoint a head coach who has not had some kind of international experience.

Rennie's options would be to hope he's offered some kind of assistant role with the All Blacks in 2017, or to look offshore for the experience he needs with a view to strengthening his case ahead of 2019.

There's no question this latter route has worked for both Joe Schmidt and Vern Cotter, respectively with Ireland and Scotland. They have gained the international experience they need to be more credible All Blacks candidates should they be interested in coming home.

That will most likely prove the case with Joseph, too, if he's able to steer Japan to a place of strength at their own World Cup.

Rennie won't be the only New Zealand coach with half an eye on the international market.

Todd Blackadder has already declared this season will be his last with the Crusaders and hasn't yet hinted what lies next. He had time with Scotland in 2004 and would make a strong addition to any international coaching team.

Canterbury coach Scott Robertson would be another surely tempted to leave if he can't find a Super Rugby post this year.

With both the Highlanders and Crusaders looking for head coaches, Robertson will possibly wonder if his time will ever come if he misses out on a role this year.

The top 20 teams and their coaches
1. New Zealand - Steve Hansen (NZ)
2. Australia - Michael Cheika (Australia)
3. South Africa - to be confirmed
4. England - Eddie Jones (Australia)
5. Wales - Warren Gatland (NZ)
6. Argentina - Daniel Houcarde (Arg)
7. Ireland - Joe Schmidt (New Zealand)
8. France - Guy Noves (France)
9. Scotland - Vern Cotter (New Zealand)
10. Japan, Jamie Joseph (New Zealand)
11. Fiji - John McKee (New Zealand)
12. Georgia - Milton Haig (New Zealand)
13. Tonga - Mana Otai (Tonga)
14. Italy - Conor O'Shea (Ireland)
15. Samoa - Alama Ieremia (Samoa)
16. Romania - Lynn Howells (Wales)
17. United States - John Mitchell (NZ)
18. Canada - Mark Anscombe (NZ)
19. Russia - Alexander Pervukhin (Rus)
20. Uruguay - Esteban Meneses (Uru)