I've been wondering about the possibilities for special events and semi-unique people to acquire. I think it'd be fun to have something like, for example,
A border-crossing tunnel. You pick up on the news that smuggling efforts between surface countries are struggling with the limited avenues of crossing, and you can build a tile that connects to the other country, causing smugglers to invade from both the original entrance and this new tile. And they carry higher value things than normal, as well as being tougher and having a unique perk they generate with. Demolish the room to go back to just the main entrance and stop the smugglers coming in if it becomes too tough, or if the required tile is just problematic.
Rescues. You capture an invader and their significant other, their sibling, their parent, or just a mercenary comes through. A mercenary generates with a high level of a weapon mastery. Family or lover have a very high relationship score with the person you captured, as well as family having similar traits visually and mechanically.
Black market quest-treasure. Someone stole the birthright scepter of the elven royalty. This is needed for proof they are the crown successor, so if you buy it, eventually some strong soldiers will come in, and weather that storm and the prince/princess comes in after. Capture them, event concluded, you have a cute elf with a unique Royal Lineage trait that multiplies their sell value. It can only be inherited if their breeding partner has a similar trait though, because no kingdom is going to recognize the bastard spawn of some slave. By the time a player could get a second royal, they probably have high level, high value minions, and breeding a fresh level 1 isn't amazing money even if their base value is multiplied by the trait.
Nothing like that stuff has happened in my playthrough. It'd be good to inject a bit more personality into these minions though. Factions, relationships, prestige. There's a lot to be done in general, I know, but I hope random events like that come sooner rather than later.