Gazebo,
So i saw this mod:
http://steamcommunity.com/sharedfiles/filedetails/?id=115134695
I thought the immigration system fits perfectly into our new happiness system.
When the city is quite well-governed, protected, literate, and well-fed, it starts to absorb population from all around the world.
Vice versa,
When the city reaches its breaking point of civil disobedience, or the intense bombing and shelling forces them to become homeless, the city starts to lose population.
These people will migrate to other cities where they live a better life.
Yet, if the city gets too much immigrant it will create another problem which reduces the cities' happiness.