Not an idea for the devs so much as for the players ...
Those of us with crops who need herbs
and those of us with herbs who need crops
could meet for a weekly farmer's market.
Maybe we could have a moving market, like Estevan Meadows Veggie market on one day and a boggy neighborhood's herb market on another. I think that organizing at the neighborhood level makes the most sense. Meeting in-game to sell or swap would be fun and much different from the auctions and vendors.