A long-run prediction, as inequality inevitably increases in the same period (https://steemit.com/politics/@two6two/why-inequality-will-always-increase-in-the-long-run):
Governments of all sizes - from the smallest cities, to the largest alliances of countries - will manage who stays and who goes from their jurisdictions, the way that sports teams of today manage their rosters.
You're the top talent in the world? We don't care where you're from, we want you on our team, if you're not already here.
You're the worst talent in the world? We don't care where you're from, we want you off our team, even if you and your ancestors have been here as far as anyone can remember.
The mechanism? Likely the market.
Top talent? It doesn't need continuous handouts. It not only earns its keep on the team, paying for itself, but it makes a ton of money for the rest of the team!
Bottom talent? No continuous handouts for these guys. Since they can't even earn their keep and afford to stay, they'll self-deport - their economic situations will force them to leave.