Some crafting recipes return items to the input side of the crafting table. For example, the recipe for a cake returns empty buckets, and the recipe for copying a written book returns the original book. These returned items are currently neither visible nor searchable in JEI, though. Could this feature be added?
When an item is returned to a square in the input, give it a different background color and put the returned item in that space's tooltip. If you go this route, I think you should have 2 new background colors: one for items that are returned exactly the same as what was input in that slot (like the book), and another for items that are different than what was input (like the buckets).
Instead of showing the regular crafting interface of inputs -> output, show a new interface of inputs -> returned inputs and outputs. If this is too much clutter for every recipe, perhaps only use this for recipes that return something, and use the existing interface for ones that don't.
Some crafting recipes return items to the input side of the crafting table. For example, the recipe for a cake returns empty buckets, and the recipe for copying a written book returns the original book. These returned items are currently neither visible nor searchable in JEI, though. Could this feature be added?