It could be an interesting PrC but I would certainly put in something in there to boost AC. Possibly some sort of "Sword Blocking" technique for AC ever couple of levels? I know in some forms those that used to fight without armor, even without shields would get better at blocking blows with just the sword then a normal swordsman would be. Theres my 2 cents, hope it helps to stress the need for some kind of AC bonus, otherwise I could see a lot of people shying away from such a PrC.