In a touch of irony the Four Nations a decade or so ago they canned is probably perfect now.
NZ, Australia, England, Tonga/Samoa.
It would be a tough 4 week tournament and no more easy games for whoever was the 4th side like it used to be.
I suppose that means someone has to miss out though as five doesn't go into four.
And you probably need England playing International footy somewhere.
If you make it a 5 nations series it probably drags the tournament too long
As it means 4 games plus a final.
Would would take 6 weeks as you would have a bye in there as well with the odd number of teams.
4 teams is the perfect mix/formula moving forward it just means someone has to miss out