Many of you may have played Nethack or SLASH'EMm this idea is derived from them.
In Nethack, you can choose to take up challenges (called conducts), such as being a vegan, not eating at all, not killing anything or being an atheist. In these games, they are optional and are not binding, you don't actually set them and they are tracked until you ascend.
There's also a similar thing in Fable (or at least the first one), where you can take up challenges at the start of missions to get extra gold or something.
These could be implemented into DF, but slightly differently, for both Adventure and Fortress modes.
For fortress mode, one could set conducts for individual dwarves on the embark screen, these would be binding, so if set to vegan, they would only eat vegan food (maybe even starve before eating meat?). It could be set on a fortress level as well, so you could set the whole fortress to vegan if you wanted. Both individual dwarf conducts and fortress wide conducts would give you more embark points. Some conducts would probably change relations with different nations, so vegan might improve your relationship with the elves and pacifist might improve your relation with everyone. Setting conducts could also make skills grow faster, so a conduct where a dwarf wouldn't touch wood at all would make their mason skill go up a lot faster or something.
Some dwarves that come into your fortress could also have conducts randomly selected, probably not ridiculous ones but more mundane ones like pacifist and vegetarian.
Adventure mode is where these really come in, being a roguelike. You would be able to set conducts at the start, as there is no way to actually win the game. You would get extra attribute and skill points for taking up conducts. You would probably also get faster skill increases or something as well.
Another thing that could be added is traits, like in Fallout 1, 2 and New Vegas. Traits would give you an advantage of some sort, but give you a disadvantage as well. An example would be a trait that would give you a faster fire rate with ranged weapons, but reduced damage. Potentially, some of these could be changed in game, like the one mentioned above.