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"Just puttin on the foil" - Jeff Hanson
“In a democracy, I realize you don’t need to talk to the top leader to know how the country feels. When I go to a dictatorship, I only have to talk to one person and that’s the dictator, because he speaks for all the people.” - Jimmy Carter
I really like the gradual population move. The wrinkle I would add would be that those population points that do move retain their original nationality initially, and then go through the standard assimilation routine.
This would turn high culture into more of a double edged sword, as if your culture is attractive you'll wind up with having to deal with Zulu quarters in your cities.