I’m one of those players who compulsively reveals the entire map. I’d like to be able to have a neat looking map without having to traverse literally the entire thing like some kind of traveling salesman.
Add an item that reveals the map. It should be available after “beating” the game. Make it soulbound, and have a faction sell it at Revered reputation. Maybe the Rovers, because they roam, or Black Legion, because they have scouts, or the Cult of Dreeg, because they have visions.
This would certainly save the hassle of copying and pasting a cleared map fow file onto new characters for each difficulty (twice at a minimum).
Personally, I think the Rovers make the most sense thematically.
The map should be revealed the same way is to unlock the elite and ultimate difficult, this will make sense!
Okay, but make sure you can still see where you haven’t been yet! Like, instead of unvisited areas being completely black, they become visible but still dimmer than the places you’ve been. I would get so lost if the map didn’t show where I’ve been differently from where I haven’t…
What about put the item, revealing the whole map, into a Treasure trove? And to distinguish, in which TT the item is, let the TT glow a bit in a specific way?
One item per difficulty level, I would say.
Ah, but the traveling salesman problem is a classic problem in computer science so this request is clearly unreasonable.
No, see, I’m the traveling salesman. I walk this map, looking for the fastest way to visit every part of it. And just as soon as I’m done, I get hit with the Square of Despair.
The final boss of all final bosses, “square of despair”! 
It’s a really old thing which no one can stop since the beginning of times…
After my character died, I copied the map with a fully explored act1 to a new character. Oh man, this is so nice. Although I can foresee that copying the map will be a pain if cloud saves are enabled. Hopefully the map reveal item gets added in the next hotfix so that we may all enjoy neat looking maps.
Imagine if they introduced such a feature, but it didn’t quite work. At first, everything would be visible, but then isolated map pixels might turn dark again. At first, it wouldn’t be noticeable, but, insidiously, the darkness would spread.
