Theres no need to get all huffy just because you havent had any replies...
I like the idea in general, but theres so many different systems at work within the game, the developers would need to balance this civil war thing with them.
For example, theres lots of cheesy ways to avoid a revolting planet from joining another empire, like reducing taxes to 0 for a few turns to get 100% approval rating, or building up lots of entertainment buildings.
I'm gonna support my argument with real world happenings. As you probably know, the Senate is dominated by 8 political parties, each vying for leadership. And as you know, if another political party gets leadership above yours, you count their strengths as weaknesses instead, and their bonuses are reversed. Now, the problem with this is, if you have low approval, you will notice it during a vote for a party, as you will get less and less votes. Most military/political coups are between different political parties. For example, Saddam Hussein took leadership from the Shi-ite muslin party, because he is a Sunni muslim (maybe its the other way around). Both political parties had different views, and Saddam was a fruitcake anyway, so he took power by force.
What would be cool is this: each political party within the game has a named leader (to give them a personal side), and each one has a personality similar to the 10 races within the game. So you have 10 personalities, but 8 political parties, so this gives variety each time a leader changes. This is a bit more in depth than I can explain, but you should get the idea.
Now, heres where the civil war aspect comes in. Say for example, you are a Populist party. You have a large population, your 'good', you have a good research economy, but a completely terrible industry and are going into debt, and your military is starting to lag behind. You notice that the Industrialist party is beginning to gain favour within the senate, as is the War party. You find that as you try and combat this by trying to recover industry and your military, its too late. Youve reached a stalemate because of some reason or another. But, you still have fairly high approval.
Unfortunately, a certain political leader has other ideas, and thinks he can do better than you, so he gathers some planets (planets with very bad industry for exapmle), a few ships, and seceeds from your empire and revolts. Slowly but surely, he gains favour with planets that have poor industry, and you try and combat this with force or negotitiations (much like you do with the alien races).
And if they manage to win, you are killed and you lose.
The fantastic feeling I have about this is you have chances for political intrigue on a whole new level. You can bribe the other party leaders, you can try and alter votes, you can even assasinate them to try and upset power. What would be even BETTER if you could do this within another alien empire. Much like you can spy on them, it would be really cool if you can use monetary clout to try and destabilise their governement from within. For example, you could fund a certain parties campaign drive within the alien goverenment, assasinate other party leaders to try and get your leader to win. When that happens, you have a new leader within the alien race who owes you big time, a new ally etc etc.
This means, you could fund a pacifist leader, have him put into power, then invade that race because you know they are unlikely to fight back. But this brings backlashes with other races which I'm sure can be delved into more deeply. This sounds like something seriously worth implementing of your a modder, or can be added into an expansion pack if your the developers.
Anyone think those sound like good ideas?