Assuming that the rumoured 4-4-3-3 format is correct, and that Wales and Cook Islands get the automatic selections, and that USA and Lebanon win their pools, I would go with:
Group Stage (18 matches)
A: Aus, Eng, Tonga, USA
B: NZ, France, Wales, Samoa
C: PNG, Scotland, Lebanon
D: Fiji, Ireland, Cook Isl
Quarter finals (4 matches)
E: A1 v C1
F: B1 v D1
G: A2 v B3
H: B2 v A3
'Ranking' Matches (mainly so that lower teams get more than 2 games)
A4 v B4
C3 v D3
C2 v D2
Semi finals (2 matches)
S1: E v H
S2: F v G
Final
S1 v S2
So hypothetically based on rankings
Quarters
Aus v PNG
NZ v Fiji
Eng v Wales
Tonga v France
Semis
Aus v France
NZ v Eng
Final
Aus v Eng
This system
-has 28 games in total
-spreads out the teams across groups to ensure most matches are reasonably competitive and more importantly that the quarter finals are well balanced.
-ensures no repeat games until the final (I think :sarcasm
-and ensures the best teams get through
Whoever finishes 1st in Pool A theoretically gets the easiest run through to the final. Second place in Pool A will most likely have to fight the winner of pool B for the other final spot.