Interesting subject
I think first that speaking of northern Hemisphere as a whole is a bit of a mistake, there is defo different situations in the NH..as there is in the SH.
I would separate NH in 2 groups :
1) England, France
2) Ireland, Wales, scotland and italy
England and France have a proper championship with clubs and with relegation systems for the ones that are at the bottom of the league at the end of the season
Ireland, Scotland and Wales are a different kind and copy more the province system that is in place in the southern hemisphere.
The province system is defo the best system as it is meant to feed the national teams and we can see this with the quite good result of Ireland, Wales and Scotland during this world cup (objectively, brought to the number of rugby players and population, Wales and Ireland are doing extremely well, I know wales and Irish fans would like more but still, great results overall compare to where they are coming from).
As well the province system does not have a relegation system so clubs can focus on other things than trying to save themselves going down in a lower division.
On the paper, with the number of licensed rugby players, France and England should be ahead of everybody but they have chronic issues to make the national team and their clubs work together. And I do not see it really changing soon. Clubs have the money and the power, they have no reasons to let the players they are paying play more for the national team. Still I think england is working a bit better than France at that level, thanks to a richer federation and an english pragmatism.
Now, if we talk about SH and NH, clearly the SH is largely ahead in terms of national team result, this is not new and there is no doubt about this. In RWC and even more in summer and autumn tours, they have the best results.
It is certainly down for a part of a certain rugby culture that favours the movement over than the sheer force phases like scrums or other phases but I think it is more down to the fact that there are much less matches to play in Super rugby (it is a mix between a cup and a championship) and other national cups in the southern hemisphere. The southern hemisphere players will focus on fewer games and will be able to play with an higher intensity because they have fewer matches along the season. There are surely also different ways in the south, NZ for example has a huge focus on the national team, all their players will have a contract with their federation and this is the federation that will drive the upbringing of the player, not so much the province (or franchise).
NH is far from being able to compete against such focused organization, I'm surprised that nobody is never underlining properly the unfairness of the world rugby at that level. a country like NZ has a huge advantage over any of their competitors in terms of organizaion and preparation (because Rugby is huge there and they have organized themselves very well, kuddos to them). Australia and South Africa have fewer matches like NZ but they are not as focused as NZ about the national team (it stays very important obviously but in Australia for example, rugby union is not as big as a lot of other sports and South Africa have more clubs and other divisions, more internal divisions I would say).
I think we won't never be able to compete agaisnt the southern Hemisphere..or we would need a revolution and maybe a competition like the super rugby in Europe (IT won't never happen due to the cultural differences that exist between the french , the british and the irish). the clubs in France and England will refuse this, they are making too much money out of TV rights and sponsorship to let their treasure escape their hands.
The only real moments where we are able to compete a tiny bit are world cups because of the preparation time that is kind of equal for every team (even though it is not entirely true, SH teams have worked since 4 years in a quite healthy environment, which is not the case for NH team like England or France).
When an english team have an incredible generation of players (like dallaglio, Johnston and Wilkinson + a proper coach like woodward), they are able to compete and to be world champion on one event..However if England and France have an average generation and some crappy coaches, they get trashed and do not do better than the 10th ranked world team. Ireland has a formidable generation of players and coach, as Wales, and they are doing pretty well for what they could hope objectively speaking.
Anyway, we would need big changes to be able to compete with SH, we would need to change the way we play rugby (Scrums should not be used as a way to have penalties but more like a base to launch an attack for example) and we would need to change our organization and put on the side the different private interest that are paraziting our rugby.
For now, as the situation stands, we will need an incredible mix of favourable events to be able to win such a competition.
Lets start the work now !