I think there are many more areas of Istaria to be discovered. Most of them are places we see but don't interact with all. A flight spell would aid bipeds to go where jumping isn't enough. A swiming skill and/or breath underwater spell would open up rivers, lakes and oceans.
These changes would open up a whole new world to explore with new teh possiblity of a whole new world of challenges, like fighting undead sharks off the coast of the Eastern Deadlands.
Rocinante