A strong Nationalist state could employ dozens of explicit measures including paid repatriation but the reality is that in a real Nationalist culture life just wouldn't be as easy for those people. I don't even mean there would be anything nasty happening but in a state where say the press was honest about minority pathologies, honest about how they behave and how much they cost and most importantly in a country that was steadfastly majoritarian in complexion many would just choose to leave. Good riddance no one will miss them.

The ones who remained would be their best as well. No one is saying that France should have the demographics of Iceland and any ethnostate can take even 10-15 percent minority populations -- probably less if needs be -- but there needs to be full spectrum pressure on people in all Western cultures.