Zombie Plague
if you go into an area with zombie's you have a chance when fighting them to get infected with the zombie virus (more so if you are not wear metal armor and you were bitten ). The virus itself wont show its real symptoms until a month later. These symptoms may include:
Had a happy though about eating raw meat recently.
Craving raw meat/dwarf flesh/dwarf brain.
No longer feeling tired.
A high enough level diagnostician (5?) who checks your dwarf out will be able to see if they have the virus before these symptoms are shown, allowing you to dispose of the poor dwarf.. if wanted..
If your unable to locate the dwarf or notice these symptoms, you basically find out the hard way... with multiple new affected dwarfs with the plague. leading to multiple virus spread dwarfs before they can take there comrade down. Any dwarf who is found to have the virus will be attackable by your army.
You may also allow your population be infected.. with some interesting results..
1) Your dwarfs will no longer tire! unless they dont receive dwarf/human/elf flesh.
2) A single corpse will provide enough flesh to feed 50 dwarfs for 3 months.. and since your now a zombie civilization your dwarfs will send small armies to try to stop you.. and now the only way to gain bigger population is to infect new dwarfs, by catching them making them prisoner and biting them.. and letting them set in a jail until they turn.
Of course this idea can be expanded on
Edit: I may not of understood the game.. but i think this is still a cool idea for a mod