I don't really think this is realistic (or practical), because the revolutions system does this already (but realisitically) and it would require changing the gameplay entirely. The government and civic types increase or decrease the stability of the empire, and if you have a large empire (which is detrimental to stability), running a good economy and a certain government will keep your empire upright. All your city/unit maintainence usually screws your economy over (which actually decreases stability as well), causing lots of
in your cities unless you know what you're doing. Changing government is part of reducing
and keeping your economy running correctly. I think people much prefer the current and dynamic
Revolutions system (A multiple variable system) to bluntly limiting the empire size to what form of government.
I bet people wouldn't want to have a single thing governing how they choose their government, simply because they need a larger empire, nor would they want to
go into anarchy to capture a city in the middle of a a war.
As for this, if you mean your empire goes into revolt, there is a simple way to remedy this. You goto the top left corner of your ingame screen, click the red womans face, and you will go to the revolutions screen. Then you can see the variables affecting your stability of your individual cities, and your empire as a whole. (If you can't see the variables, click the right hand arrow on the bottom of the window) You can then remove these variables one by one, and see your stability slowly rise up again.
All fixed.