Welcome to the org!

I think what they meant to say is that making the map black would add little to the game, only being extra work to do. In EB I already the factions know the place of several cities of the map, depending of which areas they knew about (the greeks for example know about most of their old mediterranean colonies). I think it was quite well done, because for the ai it doesn´t matter (the ai is all knowing), but for the player he has to explore a bit to see where the cities are placed, but the rough shape of the map is already there present. Imho having the map blacked out would be hardly a needed feature, adding very litle to the game. Anyway i suppose it could be added later as a submod or in a later release, i understand it sort of makes sense (for example, as carthage exploring the british isles) but it hardly something that improves the game much.