Interesting chat lads. I think Rugby World Cup expansion could lead to a more interesting tournament.
My proposal for 24 team rugby World Cup:
* Six groups of four teams.
* Each group contains one each from:
6 Nations
Rugby Championship 4 plus southern nations Namibia and Uruguay
Pacific Nations Cup (Canada, USA, Japan, Fiji, Samoa, Tonga)
European Nations Cup (Georgia, Romania, Russia, Portugal, Spain and (currently) Germany)
For example (alphabetical order):
Pool 1: England, Argentina, Canada, Georgia
Pool 2: France, Australia, Fiji, Germany
Pool 3: Ireland, Namibia, Japan, Portugal
Pool 4: Italy, New Zealand, Samoa, Romania
Pool 5: Scotland, South Africa, Tonga, Russia
Pool 6: Wales, Uruguay, USA, Spain
* Winners, runners-up and three best third place teams make the second round (the round of 16), perhaps using bonus point system to better measure third place teams.
* Shield competition for the eight eliminated teams
Disadvantages:
* The slightly messy "best third place teams" system (although this does avoid the early elimination - as in 2015 - of two from England, Australia, Wales and Fiji).
* Unbalanced groups with Namibia or Uruguay rather than one of the Rugby Championship nations (although this leads to a level of wildcard unpredictability in the draw process and group stages, and anyway it's hard to imagine any of the better teams failing to qualify from a group as runners-up or as one of the better third place teams).
* An exotic minnow at the tournament, i.e. Germany (every one of the other countries has competed at a recent World Cup).
Advantages:
* Less predictable than current tournament format, while ensuring that all the best teams can compete at the knockout stages along with the best of the outsiders.
* More inter-regional matches against teams from other competitions, e.g. European teams can measure themselves against Pacific and southern nations rather than competing in a "6 Nations lite" of France, Ireland, Italy, Romania and Canada.
* Fewer mismatches. With the four-team groups, the best teams should usually face no more than one outright minnow - along with another Tier 1 nation and a Pacific Nation - in the group stages.
* Every team has something to play for. For example, Spain overturning USA or Uruguay and sneaking into the second round would be a landmark achievement in Iberian rugby.