Immigration/Emigration

Fairly certain this belongs here, and that this hasn't been mentioned directly before on this particular forum, but how should immigration/emigration be handled?

For those that don't know, immigration is the act of entering a new country, while emigration is the act of leaving one. Populations don't grow by births alone, in the early Society Stage it'd probably be practically the case since there's no methods of mass transit available, and it's seen as better to stick close to food sources, which societies at the time provided easily. Any form of immigration would probably be more in the form of nomads wanting to join your society, or members of other nearby tribes very early on. But as people gain the ability to traverse the globe, they also hear about the quality (or lack thereof) of life in other places, and this can spur them to try to get there. People have many reasons for wanting to go to/leave countries in history, I'll list some of them below:

• Lower/Higher Quality of Life
• Safety (from war, famine, an oppressive government
• Wanting to experience life in a different culture
• Work

And many other reasons I'm sure I missed or fall under one of these umbrella terms. Would it be worth it to model this kind of attraction in later stages of the game as mass transit becomes available and the world becomes more and more known, becomes "smaller" as it were? It provides plenty of opportunities for events and such, like cultures clashing in a single society, or could add on to a nation's identity as a melting pot of different cultures.

My initial speculation on a form of implementation is as follows: Immigration rates could be dictated by a sort of "attraction factor" that takes into account the average quality of life, safety (how often wars happen, how oppressive the gov't is, frequency of major disasters, etc.), and opportunities for work as well as other similar factors that influences how much immigration/emigration your society deals with. Of course, this runs into the problem of a nation that is oppressive might drive away all of their citizens, which would be pretty much a losing game for anyone trying that route. Now, if I remember how some things in the Society Stage might work it would probably be possible to set certain policies on immigration and emigration. For example it could be possible for a nation to have borders open to immigrants, but impossible for anyone to leave. Of course, such a policy would probably be a turn-off for potential immigrants, but that'd be a feature, not a bug.

Of course, this could also  be very hard on processors for all I know, keeping track of so many things for algorithms, but I'm not a programmer so I can only guess. How does everyone else think such an issue could/should be handled? Should it be somewhat in-depth for realism's sake, handled simply and arbitrarily, or not taken into account at all?