You can't have lock ins. Maybe borrow the UEFA seeding system. We will see more geopolitical changes in Europe over the next 25 years.
Imagine if Yugoslavia [Croatia, Serbia, Bosnia, Slovenia, Macedonia, Montenegro] were still together. They reached the Quarter-Finals in their final World Cup appearance
Imagine if England had players from Scotland, Ireland, Wales and Northern Ireland
Imagine if Czech Republic and Slovakia were together
Imagine if Russia had Poland, Ukraine, Estonia, Latvia, Lithuania players
Imagine if Sweden, Denmark, and Norway had 1 team
This is the major advantage South America has had up to this point and might still hold onto because Europe will continue changing/improving socially.