Sometimes I see something for the first time and decide that I very much enjoy it. This should apply to dwarves as well.
I propose that preferences for foreign items/materials be hidden on the dwarves preference screen and not chosen for demands and the like, but appear some short time after the dwarf in question first observes the thing. This would also make it possible for the dwarves to have preferences for spoilers without breaking any continuity from them never having encountered them.
Also certain classes of things should have some chance to start hidden and some chance to not. Things that dwarves may or may not ever see. Above Ground plants, for instance.
It would also allow dwarves to have preferences for things very difficult to obtain without forcing a player to go crazy trying to gain access to that thing. Such as rarer ores or alloys that not all dwarves may have encountered, fantastic animals they've never heard of...
I've noticed that I'm starting to talk in circles, so I'll stop it there. Thoughts?
I know this will make choosing nobles harder, since you have no way of truly identifying a no preferences dwarf, but I firmly believe that the overseer should not know whether or not a dwarf likes something if even the dwarf does not know. And you don't always know what you like, so this does seem logical to me.