I like this idea.

We could think of expanding the Four Nations to a Five Nations. Have the undercard as a Five Nations qualifier tournament to be promoted to the five nations for the next season, with the bottom club in the five nations dropping back down to the qualifier group. Games can be double headers which would appeal to more players to represent there countries.

I'd expand to Five Nations purely because we know Aus, Eng and NZ will more then likely be the top three so having another team in there will give the newly promoted clubs a chance of staying in the competition.

i think to make it a success we have to set up the games to avoid blow out scores if we possibly can. all the memorable games in this WC so far have featured close games, or stirring comebacks

True but at the same time we need to make more competitive and attractive games to keep the top players from changing countries. Too many players are only playing for some countries when it comes to the world cup and the only way we will see the big three stranglehold broken is if teams can build a national side for years to come. Once the stranglehold is broken the rest will follow IMO.

If its down under, and the 4th nation is PNG for example, then there could be a Pacific Cup tournament played alongside it as double headers featuring Fiji, Tonga, Samoa and Cook Is.
Simple as that for next year.

Alternatively you could say that smaller teams need big game experience against quality opposition if they're to improve - that's the train of thought in most sports, at least.

Fans will love watching close, intense games between 'second tier' nations and it will help the games international profile, but do you think it could hinder at the same time?

I think there are a few teams outside of the 'big three' who would be better served by regularly playing against England, New Zealand and Australia, regardless of how one-sided some games may be.

I do like the double header idea mentioned earlier though!