
Three posts in one morning! After this I might have to go lay down.
One thing that is often seen in the sword & sorcery literature and artwork that is not directly included in B/X - or any other version of D&D - is the loin-skin wearing barbarian or chainmail bikini clad amazon wading into battle.
Now the argument could be made, and quite convincingly I think, that the increase in hit points each level actually does reflect the ability for an unarmoured character to avoid getting hit. But, an idea I have been considering to accommodate for this standard S&S trope in a way in which players might be happier with than just the increase in hit points every level is that a character's Armour Class can improve as they go up in levels as long as they are not wearing any armour.
DRAFT ONLY

Unarmoured AC is adjusted by Dexterity Armour Class Adjustment.
The idea behind it is that Fighters can hit an unarmoured opponent Fighter of the same level 50% of the time and the unarmoured AC progresses at the same rate as the improvement in the Fighter's "to hit". So as per the Attack tables on page X26, a level 1-3 Fighter hits AC 8 50% of the time, level 4-6 hits AC 6 50% of the time, level 7-9 hits AC 3 50% of the time...
From this base line assumption all of the other classes are worse and improve slower. I would also strongly consider not allowing this ability for any other classes besides fighters.
The key is that they must be unarmoured - wearing any armour including as shield makes the character use the standard AC system.
Art Used Without Permission

