I've always been struck by how migration is sort of all or nothing in the default version, so you're either getting slammed by waves of new migrants or getting none at all through a modified pop cap. Would Hill Dwarves coming in have any impact on the whole migrant situation?
There was something Toady said a few months ago about having dwarves that would emmigrate back out of your fortress if the economy went south on them...
Let me see if I can find it...
Would you even consider changing the relationship that the player has with the dwarves right now (as unquestioned overlord and direct allower and denier of all things dwarves can and cannot do), so that dwarves can become more autonomous and individual, and possibly create a better simulation, while on the other hand, potentially dramatically upping the potential for Fun because dwarves are stupid and very likely to hurt themselves unless continually babysat, or perhaps more importantly, if it meant that the player had less direct control over his fortress, and had to rely more on coaxing the ants in his/her antfarm to do his/her bidding?
Our eventual goal is to have the player's role be the embodiment of positions of power within the fortress, performing actions in their official capacity, to the point that in an ideal world each command you give would be linked to some noble, official or commander. I don't think coaxing is the way I'm thinking of it though, as with a game like Majesty which somebody brought up, because your orders would also carry the weight of being assumed to be for survival for the most part, not as bounties or a similar system. Once your fortress is larger, you might have to work a little harder to keep people around, but your dwarves in the first year would be more like crew taking orders from the captain of a ship out to sea or something, where you'd have difficulty getting them to do what you want only if you've totally flopped and they are ready to defy the expedition leader.
Hmm... I remember it giving more of an impression that they'd actually just up and leave... Maybe there was a DF Talk where he said something along those lines, as well, but I can't remember good search terms to datamine from DF Talk, since he apparently didn't use words like "emmigrate".
Anyway, I can't come up with good proof of it, but I recall Toady saying something else that gave an impression of having dwarves that would be willing to just up and leave for the hills in the villages around your fort if there were no rooms left or it was too expensive or the economy was bad and they couldn't get a job.