Well, if you're surrounded an enemy province, you're either:It seems lie you could exploit that. Surround an enemy province, let it rebel and wait for the rebels to enforce the demands while refusing military access.
a) very lucky
b) stronger than the enemy country
So the "exploit" doesn't sound too strong. Of course, some intreprid EU4 player will prove me wrong
What you mentioned is actually a valid strat, used for example against disjointed countries such as the Palatinate or the Timurids (the Timurids tend to break into separate regions in most games).
Well, most rebels actually don't need to hold the capital - just a certain number of provinces. Once they reach that threshold, the timer starts ticking down. Nobles, peasant, patriots, nationalists, etc. Even pretenders don't need the capital - those are the most rigid and they want 50% of the provinces occupied. I don't remember about zealots. See here for more details: http://www.eu4wiki.com/RebelRebels usually neeed to hold the capital to get ticking demand-score. I didn't think revolutionaries got ticking demand-score from any province, but may be that allow them to be more hurtful than mere peasant.