I see rivers and to a lesser extent, lakes, as indicative of an aspect of Elemental that really bugs me, that you can only, "work," resource tiles.  We have land that is green with grass growing.  The land has flowers, ferns and trees, yet I can't plant fields of wheat or any other crop.  I can only plant on, "fertile," squares, even though by any semblance of observation, your area of influence contains fertile land, or weird magic-barren-alien, terrain like the non-man kingdoms.  As far as I'm concerned the, "fertile," aspects should be special produce or production.  A sovereign should be able to plant, plow, and sow a field as long as the ground as, "revived."

I see the end result of the Stardock's above design naturally flowing into their water or river problems.  Rivers or large bodies of water are just cosmetic.  I don't know if they can do any thing with water yet.  Shoot, they don't even have a reason to produce navies yet.  I haven't seen any thing other than super continents.  I am wondering what they are working on for the expansion.