Great idea!
There is also another similar system in a relatively unknown RPG called Siege of Avalon, which attributes points of several types of damage for each weapon. So, for example, a sword would have 1-10 slashing, 1-4 piercing and 1-2 crushing. The armours have protection for all types of damage as well, so an armour could have something like 8 prot. for slashing, 3 for piercing nad 3 for crushing. Therefore, if you hit that armour with the sword, you would do 1-2 points of damage from slashing, 1 damage from piercing, and no damage from crushing, resulting in 2-3 damage overall that went through the armour. The system is a bit more complicated than that in fact (you have invulnerability rating on armour expressed in numbers, i.e. an amount of damage that it would stop completely, and a protection rating expressed in percentages, i.e. the percentage of damage above the invulnerability that would also be stopped), but that's the basic jist of it.
And yes, I know this would be even harder to implement, but this is a suggestion thread for ideas, right?
