If you were going by an init thing, you could simply set the "Vanilla default" mode to be that "current migration /40" number, and then have a init modifier that multiplies migration waves by X percent. Hence, you could just say "I want 4000% migration wave size" to get the insane levels of migration we have now.
It's just like with the minerals, though.
The game was never meant to give you every single mineral in the game in every single embark in the first place, but as soon as there were people whose first time playing 0.31.x with its obscene overflow of minerals, they cry bloody murder over the game being "so hard" when you might have to go without having more ore than layer stone. Steel equipment merely taking two to three times as much steel is making the game "so hard". Now, when you can't automatically just candy-coat your entire military, there are complaints.
Not to sound like I went uphill both ways in the snow or anything, but I not only remember playing when there were no guaranteed deposits of candy, but even now, I just don't mine the stuff, because it cheapens the game to have materials so much better than my opponents do.
I have never mined adamantine for any purpose other than opening the HFS.
Everyone complains about how the game is too easy, and how they have to keep upgrading the siegers to make there be a threat, but when you talk about taking away some of the completely unfair advantages dwarves have, to put it back in line with how the game was supposed to be balanced, people only want it easy mode.
As for Ravaught's "Refactoring the factors", this is mostly a set of good ideas, although I would argue with a few of them...
First, perhaps it might be a good idea to try to infer a sort of "unused industrial capacity" from players by measuring how many jobs are queued and how many workshops are built, compared to the number of dwarves, and assume that a high ratio would mean that there are "available jobs for immigrants", which act as a migration magnet. Idlers, by contrast, should repel immigration.
This would probably work better than the relative wealth factor that would, itself, require serious economic overhauls to take place.
Fortress morale is another good idea - it makes sense to want to avoid a place where everyone is miserable and it reeks of miasma.
The game already actually does the opposite of what you are proposing on the industry front, however. That is, if you have 0 fisherdwarves (because you atom-smash them all), then the game will say "Oh no! The player's all out of fisherdwarves! Quick, send another 12 in the next wave!"
This is a big reason why so many people want that ability to just directly tell liasons what sort of jobs you are looking for - because not everyone uses every sort of job, and the game thinks cheesemakers are somehow more vital than armorsmiths, or that you somehow have a use for fisherdwarves in the middle of the desert.