I have been wondering if would be possible to add treasure/village maps on the atlas, so that it would show the X icons on the map, as well as villages and other structure icons on the world map.

that can already be done

It can? I am trying to add this buried treasure map to it and it's not happening.
I also tried on the crafting grid.

they have to have the same scale

is the map scale from buried treasure different from non-modified empty maps?

i

How did you get that info to show?
Mine just shows this.

That's vanilla tooltip. The one you have is the weird one