Your answer pleases me and I will consider it an awesome Christmas present.
If I understand it correctly, if say, a Hungarian state emerges from the ashes of Austria-Hungary, and sees a province in Slovakia that's even 10% (or whatever the minimum percent is) Hungarian populated, they will go for that province?
As I argued in in my posts, I think Paradox is correct in not to go adding such features and keep cores in the Vanilla Vicky2 static (except I presume for certain historical events). This allows them to maintain their goal of creating a largely historical Base on which modders can build. Just look at the opposite design philosophy in HoI3 having an effect on Diplomacy, rather then following HoI2's trend in keeping the diplomatic blocs largely static (never see Britain Ally with Japan for instance), HoI3 made alliances much more fluid, and people complained that it was simply ridiculous to see the USA ally with the USSR and other such combinations.
Likewise, allowing for fluid, dynamic cores in Vicky2 could yield such ridiculous results as an AI Austria ruling all of Italy as if it were it's homeland, the USA controlling all of Mexico and the Mexicans not revolting, or Germany having cores in China. Such things are better left to modders who have the vast amount of time required to fine balance such destabilising systems. Also, it allows players to "opt in" to the absurdity of Japanese becoming the dominant culture of Indonesia, rather then "opting out".
Modders should have no trouble creating such a system of fluid cores, however, because as King has shown, provincial population proportion can be an event trigger, and add_core can be an event effect. Expect it to be in VIPicky2.