Ok, I see what you mean, very good idea ! A sandbox is a RPG where the players can do whatever they want. The DM's job is to fill the world with characters, places and relations so that the players can interact with the world as they please. If they wander into the dragon cave at level one, well, it's a shame ...
My Kanoba map also has a hex grid but for purposes linked to the sandbox. Everytime the characters enter a new hex, they draw a card that hints on an event. The player that drew the card rolls a dice to set the danger level of the event (harmless, complicated, really dangerous). Then, that player has to describe what happens. It's the DM's work to do something with the player's proposition. In that game (Oltrée !), the characters discover the region and have to pacify it and protect the population, it's a good way to pass the narrative onto the players and, as a DM, it's a wonderful experience because, you're also a player !

I want to say that I went back to your work recently and it's truly amazing ! If you plan, someday, to do something professional with this setting, let me ... no, let US know, I'm sure I won't be the only one willing to pay for it.

Keep amazing us !