Thanks guys, I belive that it really should call for a feat chain, with quick draw being base for it, Iaijutsu really is something very stylish and is more based on getting your opponent when he is not ready than anything, since in real life you cannot survive after a well placed strike that makes it.
I would not allow it simply for the reason of not being able to take actions when it is not your turn, be it free or not. I believe thi has a lot of potential and tht we should really try to carry this to the house rules forum, if someone hasn't already...
I think that the one with the blade in the scabbard would not be considering threatenig anything, i would follow the guidelines of invisible attackers, thus if your opponent does not know of your ability you do not have problems, if your opponent knows about it he can choose to ignore you or not, the thing is that he will not have his Dex if he is ignoring you or doesnot know.
Readying an action could be a good description, but Iajutsu is more than that, in fact, it does take a kind of trigger but it is more tied to getting your enemy unready than anything, much closer to a sneak attack and a rogue with a shortword hidden with sleigh of hand.