Yeah, I don't really see anyone having access to the full plate armour.
I am hoping that it is not the case that the rogue class will make a more effective "samurai" character than the fighter class would. But I am going to have to look at it more closely. I'm not all that familier with the ins and outs of 3.x. I'll probably have to rough out some characters and have a look.
From what's been discussed so far, the majority of the problem seems to lie with the Sneak Attack ability of the rogue. I've always been slightly dubious about the ability to use this ability on open combat. I am hoping to change as little as possible for a number of reasons. Not the least being simplicity. So perhaps just restricting when and where it can be used would be an adequet solution.