Some friends and I talked about a rework for the armor system. One suggested that I post it here, so, here I am.
Let's be honest -- There's no reason to get Leather, Chain, or even Gold, Armor. I think we can fix that.
Leather is cheaply made, therefore I don't think it needs to be changed.
Chain should provide more mobility, allow you to move faster, but sacrifice some defense.
Gold breaks quickly, with no added benefit. Let's change that. Gold tools are already tied with enchanting. I think that Gold Armor should give the player more experience.
Along with this, I suggest that Gold -- Or, possibly a new armor set altogether, -- boosts critical hits. These would give proper cause to Gold's low durability.
Iron should remain the same, providing a good neutral option. Diamond, currently being the best armor set in the game, already has a good system in place with the Elytra. Thus, Iron and Diamond would likely not be changed.
With Chain, this would allow PVPers to choose between the low defense, but higher speed Chain; the low defense, but higher crits Gold; and the neutral Iron.
To me Gold and XP is a great idea but it could improve potion when worn or something possibly. Think like robes for wizards/witches are light armour compared to medium or heavy in other games and mods that add benefits (robes are weak but can have additional benefits for magic which they specialise in). Maybe Gold can be enchanting cost or potion effect beneficial in some way. I agree with your XP suggestion for Gold (crits maybe) but if I were to expand on it that's my suggestion, either way if it were XP benefits added to Gold Armour I'd be happy with that.
The chain one is really good, that or maybe more projectile benefits like not using up an arrow or more damage from a bow.
Otherwise though I agree with all the rest. While leather is good for dyes or being like overclothes in a way they are very much useless in survival but can be suitable for decor or a map to have you gain over time instead of just getting the other armour types that easily (like maybe a hardcore skyblock that gives you armour tiers as rewards besides other resources/tool tiers.