If you want some example of world/mini-map display, take a look at Gathermate2. Some parts are definitively deeply tied to Gathermate2 and should be refactored but the whole thing worths looking at. And it's GPL'd.
I have been thinking about two addons who could use such library. I wrote one of them but it just shoehorns its points into Gathermate (which allows it though it lacks a few API). This is what I would expect :
handle a separate database par addon (or even several databases per addon : identify database with an arbitrary keys, which happens to be the addon table when the library is embedded. See how AceEvent handle this),
define pin categories (associate labels and icons to keys),
add pin to any map,
remove any pin ,
show/hide all pins,
clear all pins,
provide some callbacks for user interaction (onEnter, onLeave, onClick) for both minimap and worldmap pins,
(optional or configurable) display pins only on either worldmap or minimap,
(optional or configurable) display nearby pins on minimap border,
(optional or configurable) hide/change minimap pins when the player gets closer to them.
I'm not sure about point categories. It fits addons like gathermate that handles several points with the same labels and icons but it could be awful for addon handling unique points.