the ability to add custom markers to the map (not just flag icons)

Adding item icons to maps will improve map navigation without cluttering it with labeled flag markers. For example, you're a player eager to mark every structure you've discovered on your map. You mark all fossils with a bone, all pilager outposts with a crossbow, ancient cities with an echo shard, villages with an emerald, a woodland mansion with a totem of undying, or any other items you choose.