Finally, a use for all my caged goblins!
Silver had a great idea. I'd like to see something like that, a bit more war-based, though. Perhaps when armies you can throw captured enemy siegers into your army to act as untrained wrestlers on the front line. Or they could be used as actual slaves for your army officers out to war, think of an happy thought 'Went to war with a faithful servant.
You could be able to assign them to wars like assigning dump or melt, just on the cage they were captured in. Or on the creature, if we'll be able to capture wounded unconcious enemy soldiers.
When you go out to war, you may actually have an new incentive to attack enemy or neutral villages - a random proportion of the town would become slaves, and former soldiers would appear with injuries from the battle, while working class dwarves that weren't killed in the assault would be ripe and ready for use.
And then whenever the civ for that village you just left in ruins discovers you, a great siege would occur! Oh, all the blood and genocide! Marvelous!
New room option, dragged out from bed: Slave quarters. Wounded slaves gained in war would be nursed here. Unless certain cultural limitations say not to, slaves would be confined as beggars, sleeping in the halls unless assigned private slave quarters.
Apparantly I'm feeling were warlike right now. I'm sure I could think up some other uses for them besides small undesireable work like refuse hauling. They might even be the same as dwarves, just disrecpected and shunned from society.
But just imagine the legends this would cause! How much more epic would it have been if Cacame had been a slave at first, and earned his freedom?
Also tentacle demons have a strange affinity for attacking slaves.