New game system: Cartography, the ability to make maps.
New items: Maps. Could be added to carpentry along with paper and book supplies.
New container: Map Case
Breakdown: I suggest this as a potential added capability for rangers or Loremaster Explorers, though this was mostly directed toward the LM knowledge as there's a lot of rangers. Add in the capability for Loremaster Explorers to make a map of the area they're in. A direct copy from the mini map. These maps could then be sold or given to other players. If a player has a map in their inventory, that area is now revealed when they enter there. A map case could be added as a container to store the maps, but like phrasebooks, they'll only function if actually in your inventory.
In addition, I think these maps should only be of main areas, or specifically not dungeons. They will not reveal anything that's hidden, or not normally on the mini map.
Let me know what you think! I saw another suggestion that involved making map fixtures. I think that would be a great idea, and potentially a way to combine these ideas. Add in an art crafting recipe to frame a map, like a painting. Or for artisans, to carve a map into a granite table, like they have in museums a lot. Could be all sorts of interesting ideas.
One last thing. If this is doable, and something you guys are interested in, it could also add functionality to the Map Cabinet fixture. Something like: the map case can only hold ten or twenty maps at a time, but you can store all your maps in a map cabinet, unlimited. But it's a fixture, a literal cabinet, so the average player isn't going to be able to carry that on their back. Could increase the weight on the cabinet for extra measure lol.
I look forward to hearing your thoughts! 
Toodles!