I like the idea, just maybe with a quick adjustment. It could be easily exploited if it were by province. If say I were Austria, and I was getting tired of Hungarian Nationalists interrupting my wars every few years, I could potentially release a single province to Hungary, and I could end the nationalist rebellions. Maybe a region-by-region system would work, but at the same time, may also be possible to exploitation, as there is no "patriot" type rebels a la EUIII (to my knowledge)
Then you would just get hungarian patriots plus someone to support them