Well I've searched for both of those keywords and found nothing relevant on the first page or two so I suppose I'll continue writing this out.
At first I wanted an option to reject migrants because the game would get so laggy for me around 70-80ish (but I just decided to limit the amount, figured that's good enough). My initial idea was to be able to sacrifice them to Armok and in return we get some sort of artifact for doing that. Then I was thinking of a 'happier' way of getting rid of dwarves (since sacrificing is not very nice, but hey, sometimes the ends justify the means). I was thinking that certain dwarves after reaching the climax of their life (they become legendary <insert job title>) you would be able to select something in 'v' 'p' that says they are allowed to begin preparing for ascension. After this happens it will give dwarves happy thoughts because it would be an honor and what not to ascend (or descend, whatever floats dwarves' boats). After they do this they are removed from your fort and they leave behind a legendary item pertaining to the job they mastered (can be in the form of an artifact) and as long as this item remains in your fort, you will get bonuses to whatever aspects. They should be sellable or at least have some way to toggle them on and off (elaboration on this further down)
For example a miner dwarf who ascends have a chance of leaving behind artifacts that make all dwarves mine a % faster or each time you dig one tile in more stones are revealed rather than the ones directly adjacent to you. Something like that. Some of the artifacts can be cursed and have negative effects, and some can be both. Military dwarves can leave behind an awesome weapon or piece of armor, some can attract larger waves of enemies during sieges/ambushes or increase the chances of a megabeast appearing etc...
(elaborating on toggling them on and off) There are many things this can be expanded. We could have a building ascension or altar that has to be built INSIDE rock (just like magma forges have to be built on top of one open magma source, this would have to be built on top of unmined rock, so I guess like a wall carving but more graphical). Anyways, This altar could have open slots where you place left behind artifcats by the ascended, placing them on the altar would activate their bonuses. This can also be a way to sort of balance out having a million bonuses but most of them should have at least a minor downside so if you stack them up the negatives will continue building up as well.
I had another idea but I forgot it, figured I would throw this out before I forget it as well. So this idea was meant to get rid of some dwarves but bring new, possibly "fun," features to the game as well.
-------------
One of the other suggestions I had. I was joking with my friend that we need a "hulk smash" skill to get rid of rocks. Then I thought why not have some sort of rock crushing machine (like those huge noisy things you chug wood in and it comes out as saw dust or something). Granted it wouldn't really speed up removing stones from living quarters significantly but it would be better than dumping them then reclaiming them all. And we could have some use for the dust/crushed rocks. Sort of like sand but maybe for some other uses. Or we can just have hulk smash and be done with it, nothing left behind.