In the last game I played I was stuck in a loophole where the players could not win because Harkonnen would simply declare a duel an win the duel all the time.
Some players said that duels are actually almost never used except for the game ending where you know that it will always be ending a s duel.
So my friend has a suggestion that does not makes much sense but that would make the game play much more interesting.
Duels cannot be declared if the player is going to win. So if the invasion would make a player win, no dueling can be done.
So players must try to declare duels before the player get in a situation to win the game forcing players to use duels sooner in the game. That would also change the balance of power since people will lose leadership faster.
I don't know what people think about it, but it looks pretty neat and it might increase strategy due to forward planning.