This is great!! I love the idea of needing Arrows!
I am sorry.... but to the complainers who are saying "I don't want to be forced into a certain play style because I ran out of Arrows" DON"T PLAY A RANGER!
They already stated that each archetype is going to feel different, and if I am playing an archer with cool mechanics I damn well want to feel like an Archer, and that means I don't have a magical butt hole I pull Arrows out of that never runs out! If you wan't to play a ranged class that doesn't run out of projectiles they already have that ! It's called a mage, and they probably don't have as cool of tricks as the Ranger who comes prepared.
The only concern I do have for the ammo is the idea with the decaying world. Will it still be easy to make arrows come winter time when resources are close to depleted? If its not "easy" to get more arrows come time when resources are starting to become limited, then there would be a problem as too why play an archetype that you can't play to its fullest ability come later down the road (goes with traps too).
I love the mechanic but a ton of thought needs to go into the crafting system and the resources of the world for these things.