Let me clarify.
Even in the Conan RPG, a barbarian in a loincloth really isn't as near as effective as a foe wearing a breastplate. I'm not saying the game should allow that to happen (although, in my zest to make the point, it looks like I am saying that in the OP). Hell, when he can, Conan wears armor in Howard's stories.
The point I am trying to make is that I'd like to see, in 5E, it be a viable alternative to not wear armor--to have a decent chance of surviving not wearing armor.
In D&D, as it stands now, a fighter could never survive long with no armor because he's be considered AC 10 (or so) and too easily damaged.
I want 5E to have a way that a swashbuckler in a cloak, a barbarian in a loincloth, and a dueler wearing a baggy pirate shirt, carrying a foil, all have a decent chance of surviving adventures. I want that type of character--the no armor character--to be a playable choice.
I don't expect the character type to be able to be as good, toe-to-toe with a heavily armored chap. But, I want there to be advantaged and disadvantages to wearing armor. If you decide not to wear armor--and the thief might--then you've still got a decent AC via the character's DEX and Dodging bonuses.
IMO the way to do that is armor as DR and active defenses.
A parry defense thats an opposed attack roll and a dodge defense thats rolling a reflex save versus the attack.
That way if a lightly armed character would have a decent chance of avoiding being hit by an attacker with equal skill and a great chance against a lesser opponent.
I've never understood why D&D doesnt use a system like that though honestly. Its how i usually houserule 3.5 games and its worked out great for years.