ShameJax

I hate this youtuber now but the concept is there - I rather hate that the tools would have to be unbreakable because the slightest durability change would cause it to break. Also, I don't have the ability to edit the resource pack. Interesting, but I think I would like to see less... ghetto methods of doing this

Could some other metadata with a description to describe it's durability be used? 

Metadata is a thing but it isn't persistent. If we could assign textures based off of NBT data... well. We have a party on our hands. LotC's core mechanics revolve around a clever usage of NBT.