Now that Entities are starting to learn, write and talk about the world, (at least superficially, which will hopefully have an in-game impact soon.) I think it'd be a good time to bring up the possibility of persistent mistruths, myths and legends that just never actually happened but get repeated as scientific/historical fact anyway.
In a world of magic like DF tends to generate I figure there'd be a lot more superstitions than our relatively magic-free world; especially if there's no plans for "predictable industrial magic" that will always work the same way- people you tell about the pond that randomly boils away in the full-moon will be more likely to accept that it actually happened and if your word is proven wrong, maybe even invent variables you didn't account for when you "witnessed" it yourself which then get added to the superstition when they tell someone else.
Mechanically, I think this could tie in with lying, just relying on general world data instead of personal entity data. Functionally, I'd like to see things like procedurally generated "snake oil" effects, semi-rare circumstances where otherwise worthless materials become valuable because potential customers falsely believe that the substance has supernatural properties like "good luck" or "disease immunity". Some in-game reference about what superstitions your civilization has would be nice to see, but I'd settle for some conversation options and/or just an occasional price inflation in the trading screen.