Hello there.
I'd like to present my little idea I had during a long walk.
I think, as many have discussed before, that there should be a possibility of non-dwarven immigration. While the people immigrating should be able to do all the jobs accessible to them, there should be an option to declare different laws regarding non-dwarves. Here the player can define in which way the dwarves let them interact with them, eg. He decides that all humans must become furnace operators. Furthermore he could have no laws, which would increase or decrease tension between the two different races. Every bad thought produced by a member of a different race should add to a prejudice score. So if a dwarf feels sad because a human insulted him or killed a friend he becomes scornful. After a while a trend could cause upstarts and riots amongst your people. They would try to force them to leave. On the other hand, through good guidance, they could become loving and dependent on one another, Which would be incredibly difficult to maintain a good functioning happy elve/dwarven fortress.
A different way to rule your migrants would be by noble hand. This means that the higher nobles are able to create laws for immigrants. This could range from having your elve ladies being forced to dress in leather tongues and high heels, or it could mean that humans could rise to nobleman level, depending on your prejudice score. Prepare for fun, when your noble wants all Elves to become woodcutters.
In addition i'd like to see hobbits added in. They could begin building hobbit huts in your land, possibly destroying your well laid out underground passages, and other fun, but they would be very adept at making certain luxury products as hats and tobacco. Hobbits and dwarves should get along rather well in the usual, unless they destroy their rooms and furniture.
So how do you like my idea?