GalCiv2 had a very rough allusion to oppression in that certain Government Types could raise more in taxes at the expense of requiring higher approval levels to stay in power. I think it'd be interesting to see this taken a step further, and allow rulers in Elemental to have varying levels of oppression on their people. Higher or lower oppression have different costs/benefits:
Oppression:
Pros:
Lower chance of rebellion
Can cut off trade to other kingdomes
Can conscript troops more quickly and more cheaply
More black market activity
Cons:
When rebellions happen, they're worse
Other kingdoms/empires won't like you as much, especially if they have low oppression
More black market activitiy
As always, thoughts and comments are welcome.