Just throwing this out as a provocative thought here to be shot at...
First, hold the World Cup every FIVE years.
Years 1-3 in the cycle would consist of four "world region" competitions, each of six nations. These would be run as per our six nations competition currently, i.e. home one year away the next and tables recording results.
Pacific Nations -
NZ, Aus, Fiji, Samoa, Japan, Tonga
Americas -
US, Argentina, Chile, Uruguay, Canada, Brazil (There is precedent)
Europe -
Eng, France, Wales, Scot, Ireland, Italy, (As current 6 Nations comp)
Europe/Africa -
S Africa, Namibia, Georgia, Romania, Spain, Portugal
Plus , in each year, 1-3 of the cycle, nations may play any 3 touring teams from other world regions ( so if they wanted S Africa, which is in a relatively weak regional competition could still play NZ, France and England if they wished.)
Year 4 of the cycle - No regional competition (this allows forward planning of WC groups and arrangements. Nations would know their WC group at the end of year 3). In Year 4 Nations are free to play up to five touring sides of their choice at home and tour up to five other nations as many times as they wish, but opposition must always be from another world region. Within this might could be added a system of play offs, home and away for the bottom team of each group after three years and any new contender from the region.
Year 5 - World cup, no other internationals - Four groups each of six teams. Groups to comprise teams drawn from each world region seeded according to regional performance cumulatively across the tables for the regional competitions years 1-3. (e.g Culmulative leader over 3 years of Pacific Nations, plays second placed nation of Americas, third placed nation of Europe, Fourth of Europe/Africa, plus two seeded bottom placed teams randomly drawn from all four).
The top Two teams from each group qualify for quarters and then as per.
This gives a nine week competition. With this could be a plate competition for the third and fourth placed nations from each group, run concurrently with the quarters and semi finals and final.
(This all made much more sense when I was still drunk
)
What I am trying to get at is a structure which gives regular opportunity to "Tier Two" sides allowing them to get the game time to develop, whilst maintaining competition between the "Tier One" nations.
With a magazine of 20 rounds - go on!