I like the idea of charging up an attack in this case. First, you obviously need a feature that lets you draw your weapon as a free action. Then, what if every time an enemy misses you when you are using the Dodge action, the next attack you make receives some kind of stacking bonus? The idea of dancing around your opponent as they swing wildly, until at last you've fully comprehended their style of fighting, and then drawing and ending with a single highly charged attack is a really cool image. I think building the class around different ways of enhancing that one single attack as well as an equal amount of ways for you to avoid enemy attacks would make for a pretty compelling Iaijutsu fighter.