Well here the tough parts, now i dont know how far they will go with this even if they will listen to players or not. When i played Master of Magics it was ok, but lack of interests. After that i played Lords of Magics, prob the best game i ever played back then along with Planescape: Torment. When you define elementals and having more than one types besure to have solid infos about them as well what connected to that elementals. Here some details down below the way i think it should be like, some will agreed and some may not...
Elemental of Air: Frost Gaints, Ice Dragons, Tundra Terrains and Heroes. Opposite of Air -> Earth
Elemental of Earth: Gnomes and Dwarves, Ancient Dragons, Dirt/Rough Terrains and Heroes. Opposite of Earth -> Air
Elemental of Water: Lizardmen, Sea Monsters, near Swamp/Lake/Ocean Terrains and Heroes. Opposite of Water -> Fire
Elemental of Fire: Fire Gaints, Demons, Red Dragons, Desert/Fallout Terrains and Heroes. Opposite of Fire -> Water
Elemental of Order: Humans, Angels, Plain Terrains and Heroes. Opposite of Order -> Chaos
Elemental of Chaos: Nomads, Beasts, Plain/Dirt Terrains and Heroes. Opposite of Chaos -> Order
Elemental of Life: Elves, Fairy Dragons, Grassland/Meadow Terrains and Heroes. Opposite of Life -> Death
Elemental of Death: Dark Elves/Undeads, Bone/Ghost Dragons, Dirt/Desert/Fallout Terrains and Heroes. Opposite -> Life
That what i was thinking about and it seem logical and straight forward. All these factions that are opposite consider hate each others while neutral to others. Dilpomacy and Espionage as well as Religions that change the face of the world.
Hope this help, looking forward to play it someday 
redindus