Wandering Traders

You could make it so that when the Wandering Trader spawns he wants to buy items from the biome he is spawned in and sell items from biomes the player has not been to at that time. If he has already been to all biomes, he sells items from the biome that is furthest away from the spawn location I think this could be very useful in the early game to get items for which you would have to explore for a long time