I've been looking for a while, and have yet to find a resource pack that uses the custom durability textures to add different clothes. Does anyone know of one?
No, because it's not really possible. The system for using durability to make custom textures only works for items in inventory. It can't change how the item looks on the player. So even if they make an icon that looks like a suit or whatever, it'll still be the normal armor texture that people see on the character's body. Sadly this system is horribly limited in this regard.