And why would Turkey represent the Middle East & North Africa? Apart from ottoman rule/ religion in some areas, Turks have nothing in common with those people. How can Turkey represent Iran for instance, and how is that fair?
Same with Brasil. You will let the only Portuguese country in America represent all the Spanish countries?
The world is not that united as you would like to see.
It's not about ethnicity or having much in common. Victors of WW2 setup the security council. World has changed today. It's about states that has strong economy that can best represent a region. Japanese are a minority in North East Asia but most nations would accept it representing Asia-Pacific due to it's strong economy & to some extent due to it's growing militaty strength. Australia/New Zealand would be seen as an extension of Europe (already represented by Britain, France), hence very unlikely be supported by any Asian nations.
Either Brazil (largest economy in South America) or Argentina would be a good candidate. But many nations in South America still views Argentina as being too euro-centric, hence Brazil might have a better chance.
If Iran was not under sanction, It might had the strongest economy in Mid East and North Africa. But it's economy is in shambles. Israel will not be accepted by anyone. Arabs have no concept of democracy and minus oil they barely have any economy. It lives only Turkey a democratic state with a flourishing economy and having good ties with all sides (Arabs, Iranians, Israel, EU & Russia) that might represent the region and would acceptable by the majority.
Same goes for sub-saharan Africa. Nigeria, South Africa or any other nation picked by Africans could represent that part of the continent.
This way entire humanity is represented. Offcourse that's utopian thinking. Very unlikely Washington will allow any expansion of the security council as that will sign decline of it's clout !