When
I mentioned my idea of an elemental civilization a few days ago, Ahwaric told me it would go with eastern civ. I wasn't totally convinced it would go along. I'm still not convinced. But I would like to share my ideas here...
First, there would be 4 leaders, one for each element (5 if Ice). The palace would provides 3 mana according to the leader. For example, if Leader A is Air and is played, the Palace in the capital would be 3 Air. If it was Leader B (who is Fire), it would have been 3 Fire. Every unit (that hasn't already a predefined race) would gain the {Element} Elemental upon production.
The thing is that a national wonder is available at some tech that give the possibility of using 1 {Leader} Mana in exchange to another mana that isn't {Leader} Mana. Only one of each wonder can be built in game. The point of having multiple but different elemental mana is that the "elemental" units can
change their "race". They can shift to Water element and thus totally change their purpose. The point of having multiple but same mana is to enhance the power of your units, in exchange of a more rigid gameplay.
Lorewise, they would be humans "touched" by the power within the mana nodes, particularly by the elemental ones. At first, they would not have "learned" to use their powers, instead they would rather live with it. Only time, research and experience could grant them, say, a powerful promotion giving them +1 affinity for some mana.
Having written all of this, I'm still not quite sure it would fit with what has been discussed about the eastern civ. There would be no "summoning elementals" thing since they
are, in a way, the elementals (btw, the summoning spells would certainly be different for them).