In my Ireland game my current character has gotten the lunatic trait again. Still waiting for a funny event to happen because of this.
The strategy I have devised to cull powerfull vassals is to strip them of excess/all titles once I reach a high age and death is approaching anyway. They'll hate you for it but that's only temporary, once you die, your successor loses those penalties
Yesterday I had a very satisfying moment. I pushed my uncles claim to the french throne and after a short war I crushed the current king of France and made my uncle King of France.
Should be a powerfull ally in my future conquest of England. Also I hope to remarry my uncles line back into mine to add the crown of France to my assets as well. If I;m lucky I might even pick up the inbred trait from IT