Blank Items

These would be items, blocks, and entities that are unused by default. Datapacks and resource packs could add their own uses, textures, etc. without overriding existing features. Ideally, tags or configs could be used to assign existing properties to these (durability, entity collision, waterloggability, damage...).

*There have been similar suggestions to this, but I think this one is different enough to be worth writing.