Saw the update post. I wonder whether rather than having it so you can request that the next trader bring x resource, you could have it so the more of a particular resource you buy from a trader, the more likely they are to bring back more of it the next year.
In my current game in arid highlands, I am buying all the clay I can get/afford. If the traders had a bit of business acumen they would bring more and stop trying to sell me the tallow and hides that I have coming out of my ears!
Love the game - thanks!