Long post, sorry. But would rather get people's feedback on here than another platform.
This assumes we only have 18 weeks or so between late February and the July Inbound Tests…
If we're serious about involving the Japanese teams, then here is a different sort of model that might be a way forward, and suit the preferences of both Australian and NZ, as well as the broadcasters. It is not a new model, but one based upon the highly successful European Rugby Championship.*
It involves having separate domestic comps with a champions league. But instead of having the champions league played after the domestic season, it would run throughout the domestic season and be played on designated weekends. I'll come back to what this structure looks like later.
But basically, the champions league would be divided into three divisions: Cup, Shield, and Plate (for want of better names).
In the Cup division you would have the top 2 teams from Super Rugby AU, top 2 from Super Rugby Ao, and top 2 Japanese teams. In the Shield division you would have the next 2 best teams (3rd and 4th) from each domestic comp, and in the Plate division you would have teams placed 5th and 6th from each domestic comp.**
Within each division, you would play everyone NOT from your own domestic comp once for 4 games + 1 bye each + a final = 6 weeks total. And you end up with a Cup, Shield, and Plate winner.
I’ll explain why the byes are important further below. But here is an example of what the format for the Cup division would look like based on this year's results:
Round 1 (H v A)
Japan 1 v Reds
Brumbies v Chiefs
Japan 2 v Crusaders
Round 2 (H v A)
Brumbies v Japan 1
Chiefs v Japan 2
Byes: Crusaders and Reds
Round 3 (H v A)
Reds v Japan 2
Crusaders v Brumbies
Byes: Chiefs and Japan 1
Round 4 (H v A)
Chiefs v Reds
Crusaders v Japan 1
Byes: Brumbies and Japan 2
Round 5 (H v A)
Reds v Crusaders
Japan 1 v Chiefs
Japan 2 v Brumbies
Round 6 (H v A)
Final (1st v 2nd).
* The European Champions Cup is actually only played over 9 weekends spread throughout the English Premiership, Top 14, and Pro 14. There is a second division for all the teams that don’t qualify for it.
** Side note: rankings for the champions league are based on the previous year's domestic comps. If a team wants to move up into a higher division of the champions league, they need to improve their position in their respective domestic competition.
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Now if Super Rugby AU and Super Rugby Ao are played as a home and away double round robin with six teams each, including finals, you would need 12 weeks. No byes are needed because they would be included in the champions league (see below).
I’m not entirely sure how Japan plans to structure their domestic comp. However, for Australia and NZ: 12 weeks for their domestic comp + 7 weeks for the champions league = 18 weeks. A perfect fit.
Now, as I said above, instead of playing the champions league after the domestic comps, you would follow the European model and play the champions league on designated weekends during the domestic comps. So for example:
Weeks 1-2: domestic comps in each country
Week 3: champions league round 1
Weeks 4-5: domestic comps in each country
Week 6: champions league round 2 (byes in each division)
Weeks 7-8: domestic comps in each country
Week 9: champions league round 3 (byes in each division)
Weeks 10-11: domestic comps in each country
Week 12: champions league round 4 (byes in each division)
Weeks 13-14: domestic comps in each country
Week 15: champions league round 5
Weeks 16-17: finals of domestic comps in each country
Week 18: final of each division of champions league: Cup, Shield, and Plate
With this model, every team from Super Rugby AU and Super Rugby Ao is involved in their domestic comp and the champions league at some level. And every team from Super Rugby AU and Super Rugby Ao gets a minimum of 7 home games each year.
The byes are only during the champions league so that Australia and NZ can each have three games across each weekend of their respective domestic competitions. And having byes for two teams in each division of the champions league on certain weekends would still provide six games over those particular weekends. This is good for the broadcasters.
So we get a full domestic comp in each country (yay for Super Rugby AU!), but for those who felt a six team domestic comp would get a little stale, this structure totally takes care of that. And for any Kiwis who were worried about the intensity of Super Rugby Ao and potential player injuries, this structure gives the NZ teams plenty of 'breaks' throughout with games against the 'weaker' Australian and Japanese teams. And finally, I think it would be favourable with the broadcasters and private investors, especially with the Japanese teams involved.
Next step: invite Japan to be part of the Rugby Championship.
Side note: if for some reason the Japanese teams are not involved (at least initially), it would still work just as well for Australia and NZ. Only difference would be, in each division of the champions league, you would play the other teams NOT from your own domestic comp twice, home and away, for the same amount of games.
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One of the drawbacks of this model might be that for any given Australia team, they would only play two of the NZ teams rather than all 5 (or 6 including M Pasifika). The same might be said for any given NZ team playing only two Australian teams. At the same time, however, this structure keeps the the best NZ teams only playing the best Australian teams, and the lower Australian teams only playing the lower NZ teams. This helps to keep the games more competitive and prevent blowout scores (hopefully!). This would be even more important for the Japanese teams involved, if they are to be competitive.