"Rebellions break out if 20% of your population resides in disloyal foreign culture provinces. "
This doesn't feel very historical. This makes it that small nations can not rebel on their own against a big empire, only in synchrony with other cultures all revolting at the same time. Take the Jewish revolts against the romans for instance, they didn't happen in synchrony with other revolts.
Wouldn't it make more sense to have some kind of meter for the organization of a revolt associated to each unhappy culture, and give them a chance to spontaneously revolt if above a threshold of organization (with more and better equipped troops the higher the organization) with a higher chance due to external problems the overlord could have like civil war or being at war with a comparetively powerful nation (now it's the time to strike!)) and lower chance due to military presence in the area.
I guess according to new casual friednly policy of paradox everything should be clear, simple and predictable. That's why we have exact numbers stated and even after reaching them we have yet another countdown bar towards war.
They call it good for players who won't be exposed to "unfair" randomness but for me it's boring. Eu4 system that gives us plenty time to prepare and tells us when exacly revolt will fire is the worst of all and it's sad that Imperator goes even further in that direction.
I agree that general or province if angry enough should be able to rebel even when overall disloyalty is below those 20% and 33%. It would make things more lively. Of course still important factor for starting rebellion/civil war should be their chances of victory.
I also don't like the fact that there is a clear division that only foreign culture can rebel for independence. According to this Alexander's Empire would never split up becouse diadochis would choose civil war only not separation.
Ambitious characters, even when they are of ruling culture, should be able to seek creation of their own kingdom. Maybe seeking independence should be allowed only for characters with ambitious/greedy trait. So it won't be too common but still possible for certain power hungry individuals.