In EU so far cores have been a very significant very binary effect, used to represent everything from traditional homeland over nationalistic tendencies to forged claims and manifest destinies. I hope that in EU4 there might be room for some more detail, such as distinguishing between the strength of these claims (like CK2 now distinguishes between strong and weak claims) and possibly also the nature of these cores, so that there is a difference between having a recognized claim to the territory and having it well integrated administratively and economically.
Somewhat related (as it also deals with your control and claims to lands outside your nation) is the whole area of vasalisation. Without having very specific ideas, it seems that there is room for variation in this area as well. From vassals that are simply tributary states who owe their overlord nothing but a bit of money, to states that are effectively substates, where the overlord would be able to control troops (or raise them in their own armies) and set foreign policy.
Somewhat related (as it also deals with your control and claims to lands outside your nation) is the whole area of vasalisation. Without having very specific ideas, it seems that there is room for variation in this area as well. From vassals that are simply tributary states who owe their overlord nothing but a bit of money, to states that are effectively substates, where the overlord would be able to control troops (or raise them in their own armies) and set foreign policy.
