*Warning* very long post, thanks for reading if you have the patience.
Ok, this is something that has always bothered me. In every 4X or empire building strategy I've played to date, they have had one terrible flaw. None of them have modeled rebellion or revolution in a close to acurate way. I have yet to play a game where civil war was something you actually have to worry about. It seems so strange to me that such a large part of human history has been largely ignored by such a game genre. This is especially true for games like Civilaztion since it is, after all, an attempt to model the course of human history in a different setting. Though I've only played Civ 3 and 4, I played those alot and neither of them model rebellion very well. In Civ three if you didn't keep a city happy enough it simply would start to "rebel". All this did though was stop production from that city until you made the people happy again. This was largely just very...very annoying. That is why in Civ 4 it was changed to were unhappy civizens just stoped working....this, though a much better game mechanic, is rediculously inacurate.
--Probably the best+most acurate mechanic for rebeillion (that I've seen) is the Total War series. In those games (Rome and medieval 1+2) each city had a happyness level that was tied to a % chance of revolting. This was based on things like tax rate, military garrison, religious conflicts, ect. If a city revolted the citizens would start destorying building and killing your units garrisoned there. If it got too bad they would kick out your military garrison and form a rebel faction in that city. The problem with this for Elemental is that 1. We don't know how minor factions will work in the game, and 2. How would this work with cities taking up more than one tile. Maybe, depending on the type of rebel army, they could rise up in different tiles. For example, lets say you are playing a fallen faction. You've just taken a Human city, and after a little rebuilding you decide you want to crank up food production to feed your ever growing army.... So you force the farmers on a few tiles to work extra long and decreased food rations for that city. After a few day the farmers have had enough. A rebel army formes in one of the tiles with a farm. You can either crush these peasants, or risk loosing your new city. Now lets say the farmers take the city from you by capturing the keep. Now they either have the option of returning to control of their former empire, or forming their own minor faction (One that is ruled by farmers and who desire to start similar revolutions across the world!!!)
*These are just random ideas, as I have no idea how any of the relate mechanics will work(or if there in the game lol). If something like this was added it would add alot of depth to the game. Besides just a cool and realistic rebellion mechanic, it would force players to really have to think when determing how to treat their civizens.
--Another game with a cool rebellion mechanic is the Europa Universalis games. Europs Universalis Rome imparticular. Besides rebell armies forming if the peasants get pissed there is another cool aspect. If your generals become too popular with the people and your armies(In the game, after fighting with a particular leader for awile, individual units would become loyal to that leader, and thus support him if he rebels), they might just rebel against you, attempting to usurp power from the senate (a la Ceasar!) or you can side with the general and try to overthrow the senate and set up and empire. This is a very nifty mechanic for Civil War, and one of the best I've ever seen. I thing Stardock would be remis not to add a system for civil war in the game. Maybe your heroes have a "Loyalty" meeter, and if it gets two low, they will rebel and try and depose you as ruler. For good measure you could also make it to where when you kill the traitor you get back any essence you foolishly gave this backstabber. This, again, would add more depth as players would have to be carful when hireing/imparting essence to heroes. For example, lets say you hire Koonan the barbarian . He is rediculously powerful, but being a barbarian, he has very low loyalty. Now the player has to decide whether to risk imparting essence to him, and/or letting him lead a very large army. You could also have a system for increasing/decreasing loyalty. Maybe you could pay the heroes extra gold to increase their loyalty, or giving them positions of power, such as governorship of a city (maybe each heroes also has traits that make him a good or bad at various aspects of running a city. This would be seperate from their battle traits. This again could be similar to the system in Total war, were when a leader is in a city they give that city certain bonuses/penalties). This would add in more decision making. Lets say you what Koonan to lead an army, so to increase his loyalty you must make him governor of one of your cities. The problem is Koonan, again, being a barbarian, has alot of penalties as a governor. Now you have to weigh the need for a powerful hero leading your army, the risk of his low loyalty, and the production/economic penalties he would impose on a city as governor.
---At any rate, a combination of these different mechanics would make the game very interesting (with some twenking to make them appropriate for the game obviously) These are just some random thoughts I had. Thanks for reading if you did, and sorry for my bad spelling!