Within CK2's Merchant Republic system there was a event chain between patrician families that could stretch over a century or two and fire off Romeo and Juliet events and ship and trade post sabotage, among other things. Almost no one ever saw these events. They fired poorly (fixed in 3) and NPC dynasties die out a lot (not quite fixed) and also most of us as soon as rivalry started butchered our enemies like pigs before anything beyond the first step could fire.

Unless the player got lucky and rolled the Karlings as rivals it is always going to be over too quickly. It is a fine and fun idea. The problem comes with incentivizing players to keep a rival around for longer than it takes to murder all of them. Solve that and you got a hit.