I think it would be very interesting if cloaks hid all of the wearers clothing underneath it. Of course there would be some clothing articles still obvious, like boots, gloves, light, held items and helmet (Unless the cloak had a cowl attached?).
It could add very well add a little more depth.
But to make this even better... you would fight VERY poorly while wearing this cloak. Perhaps by lowering hit/dam rolls and perhaps dexterity. In fact, I wouldn't think you could draw your weapons while wearing it either(Due to your sheath or scabbard being underneath the cloak). This way you would not keep the cloak on at all times; normally only when travelling or trying to keep a low key.
Can't you picture this: A man in a dark cloak walking through the bustling crowd of a city. He slips anonymously through the gates and goes into a building. The evil merchant sits at his desk, counting ill-gotten money. He looks up at the sound of someone walking in. "Who are you?", and is answered only with "...merely a messenger...", when the mysterious man rips off the dark cloak, and draws his sword from his scabbard then sends his message... medievil style
-Saiden
But hope that helps.
