I just came up with an idea on reddit.
Bloodlines.
Do you know what's awesome about bloodlines? A lot of things.
For starters. You get to get married and have kids. You get to have an army of sons, daughters, nephews, grand-sons and step-sons that are at your command, and that you have special information about.
Do you know what REALLY is awesome about bloodlines? You get to play as your descendants. Genetics and super-race breeding aside... When your character in Adventure Mode dies, you can reincarnate as your descendants, and as your descendants ONLY. When your bloodline dies, when there is nobody left that came from you, your world is deleted.
Can you imagine the awesome? The possibilities? Erradicating every sentient being on the planet, leaving your clan to rule the world. Fighting a desperate fight against an Elven kingdom that hunts down and kills everyone related to you? Gathering your own army of relatives? Breeding your super-heir with special traits and starting position? Establishing a ruling family, and playing out all of these awesome scenarios? Giving importance to your family, in magic, law, diplomacy and not only? Condemning your entire family to a curse in a pact with the devil, or creating your own order of paladins blessed by the gods?
This simply blows my mind. With addition to what Dwarf Fortress is, and is going to be... It freezes my mind, shatters it into dust, melts it, evaporates it, condenses the vapor into single atoms, makes these atoms collapse onto themselves becoming both matter and anti matter thusly exploding in a new, few trillion trillions singularities creating countless worlds to repeat the process in endless iterations with new features!
Edit: I may realize you can't "condense" a vapor into single atoms...