Would it be possible to add persistent custom data to items. And possibly some hooks for using the item. That way we could add special modifiers to the items such as %damage increase, frost attacks, … etc. But the idea is the programmer implements a custom data attribute and when an item is created we can attach one or more of these custom data attributes. Then when the item is used (attack an entity, or other use item events) it will automatically call the corresponding custom attribute. This would need to persist inside of the item data. I feel like this fits in similarly to how we will be able to customize the functionality of entities.
edit: Just to clarify, this is the entity system i was referring to:
edit2: Another page describing the component system:
Also does the Data API have hooks into the component entity system? (And has the entity component system been implemented?)