Well, I've been assigned the preview copy sent to Avault, and while my official preview write up will be posted early next week, let me just assure everyone that seppuku is difficult to abuse. As King points out, in a larger clan, your vassals might not cooperate with your desires for the succession of the clan's leader. I will also say that the game refuses to let you even use the function until you meet certain criteria. And the issue gets more complicated when you factor in the age of heirs, the impact of your current spouses on the ruler, and what plots your character is currently cooking. After about 8 hours of gameplay, I have not had the desire to kill my ruler even once, even when his honor started getting low. And I've had some real crappy rulers already.
When my preview gets posted, I'll link to it here at the forum, and you can check it out.