I sense a misunderstanding on the word "open" as in "actually visible on the screen by pressing tab" and open as in "completely revealed without the need for exploration".
I don't know what whist's and Marco's decision on this is, but I agree that having the map revealed should be an option and not forced, if such a feature were to exist.
Somehow I seem to remember discussions on having Deckard be able to sell maps to the player for a fee, but I don't know if it was something that was taken in serious consideration or not (I could also be hallucinating and be imagining such a discussion)