I'm going to assume Elemental will have a fog of war, just like Gal Civ 2 and Civilizations where you can discover an area and continue to know what it used to look like, but unless you have a unit, building, or special effect in that area, so can't see everything going on there currently (unlike Heroes of Might and Magic).

So, this lead me to a cool idea- let's say you explore an area and then leave it.  Last you knew, that area had a river with a bridge.  So, you decide to send an army back there a bit later, only to find that bridge is gone (because of magic).

Or you go back to an area previously explored, and instead of a flat plains land, there's now a giant mountain or impassable valley.

It would be really great to see the players be able to radically effect the landscape for strategic purposes.  Obviously, you would need a way to balance that, too.  I'd also love it if those sort of events "surprised" the AI, too.  That's probably tough to do, but it would make that a lot more realistic if the AI would base it's knowledge on what it used to know instead of just on the way things really are (so it could be surprised, too).