If it's nation based, why not do it like the Super 14 Scoring system?

Every nation team plays everybody (say over teams minus one weeks), and the team with the most total points gets 2 points (1pt for a draw).

Then at the end of it the top 4 nations vs each other in sudden death (1v4 and 2v3), then the two winners vs in final.

Gives a chance for everybody to play everybody, no?