Release any province as a vassal. Multiple religions in one province. And some other ideas

[MikeyMoon 3]

Release any province and it gets the core.

Economic status of each province, such as comfortable, wealthy, etc.
Happiness status of each province.
Revolt rate depends on economy, happiness, religion, culture.

Possible emigration from provinces with bad economy.

Each province can have several religion groups which are shown in % and several culture groups.
Promoting culture or religion consumes legacy points.
Similar to the Victoria game where you have multiple but limited focus points to promote or convert something, but this game could have limited legacy points instead.

Countries can make other cultures acceptable. 
Countries can make religion acceptable by having some kind of acceptance rate in %.
Consumes legacy points.

With legacy points being limited and used up for religion and culture conversion, you need to think carefully about whether you want to expand or improve the economy or work on culture and religion.

It will probably affect performance though.

Edited 2 hours ago by MikeyMoon