Your suggestion is based on what you perceive to be realistic society, law and economics for the world the game presents you with.
Yes.
However, when implemented, just like the creation of the universe, laws and societies and (possibly) economic systems will be unique for each world (and each society in each world). They'll also be customizable.
Look, I hate to break this to you but economic systems tend to be grounded in the physics of a universe, and if you changed the physics of the universe radically it would no longer have anything recognizable in it. Laws likewise are based on basic biology, which in turn is grounded in the same sort of hard realities as economic systems are because they are both based on scarcity. So while I can easily imagine creating an engine that diversifies minor points of ethics and traits and tendencies of a race, creating diverse gameplay and religion, when it comes to something as basic as immigration, the fundamentals here are going to be fairly similar - whether or not my race does slave trading or kidnaps the children of other races or is matriarchal or whatever because my civilizations god said, "Thou Shalt" or "Thou Shalt Not". Things like that might create additional subsystems that you could turn on or off to create different scenarios, but they will fundamentally just be subsystems - whether or not caravans show up with sentient races in cages to be enslaved, for example. Whether they do or not has nothing to do with economic migration.
None of those objections about me not actually seeing the big picture here are actually pertinent. The fact that economic migration might be turned off by a flag in event of a strict prison scenario isn't actually an objection to a discussion of the basics of economic migration or refugees (which are more like 'emergency economic migrants'). In fact, what they strike me as is objections by people who themselves couldn't and can't explain the big picture, but who are bristling at perceived criticism.
Which is why your suggestion is kind of limited right now since nobody really knows how any of that will work.
Well, at least you are honest there. And while we are at it, lets add Toady to that list of people that doesn't really know how any of that will work. How do we know? Because this game has as more subsystems that are broken now than work. This is a game defined by its bugs, where the bugs are an integral part of what has created the gameplay in the past. And I'm not just talking about the abandoned ill-thought out economic system, but core pillars of the game play like the Happiness/Stress system are broken in the 2014 release I'm playing. Right now, it's so easy to make dwarves happy that the pillar of the gameplay might as well not exist. And even a cursory examination of the mechanics indicates that in their basic structure they could never been tweaked to work, and it will always produce absurd results. The whole system will need to be ripped out. And that's not because the replacement system is fundamentally more complex, but simply because the current system is wrong. That's because Toady is clearly learning as he goes like well... just about anyone would be. No doubt if I was doing it, I'd go down even more dead ends and wrong paths.
But yes, at least you are honest in admitting that sense you have no idea how any of this other stuff will work, you have no basis for claiming whether or not my suggestions would work with that stuff that doesn't exist yet. It's fundamentally absurd to claim my stuff is invalidated by stuff whose content you don't even know, and whose specifications are still being worked out by the designer. In the mean time...
Migrants will act (hopefully vaguely realistically) according to the social, legal and economic pressures placed on them and will turn up at your site depending on what your site's role in your civilization is supposed/perceived to be.
Yes. And presumably that role that could morph depending on your relationship to the civilization. You might start out as a fort tasked to defend a trade route against goblin incursions, and such with certain constraints about that role - civilians aren't going to show up to be long term residents of a military installation, and replacements are going to depend on your relationship to the local military governor. Fine, I get all that, but whatever your current role, once your site becomes perceived as a colony or settlement, it will begin to be subject to economic migration and be more attractive to refugees - and both those subsystems will have to work. I suppose thinking about it we could add more factors (like a colony reputation system based on my colonies relationship to civilization ethics, am I known as a 'den of inquity' or a 'wretched hive of scum and villainy' or as a great place to raise a family), but they would be additional factors to that basic description I just made, with fairly small and obvious modifications of the default behavior.
Lots of people suggest without taking into account the bigger picture, which is fine I guess, all ideas are useful, but people probably wouldn't be jumping on this thread if it weren't so "the simulation is broken!!"
Well the simulation is broken. I imagine no one is more painfully aware of that than Toady. Why is it some sort of taboo to notice how broken the game is in a suggestion forum?