As world generation is becoming more like an automated game of Civilization, with religion-inspired warfare in the next version, I had the crazy idea of putting in Wonders. Large enough cities would have a chance of generating a large, huge, expensive building unique to the world.
It should perhaps wait until town architecture gets a little bit more functional, but after that it would add some nice variance to bigger cities. And plot hooks for Adventure mode, as the things would quite possibly be full of treasure. And plot hooks for worldgen; goblins get envious of the Giant Golden Palace of a neighbouring human town, attack, seize, and then either keep or deface it.
This might even be implemented into Fortress mode. An architect goes fay, and you have a new building in the build menu that can only be built once, and that you have to build soon or the architect will go even more mad and kill something. The material requirements would be randomized, perhaps giving the player the standard building material choice of which stone block to use. And then, instead of just having a regular old cave shaped like a cathedral, you will have a named cathedral that gets it's events tracked. Although this might require multi-level buildings for the more magnificent structures.