I think it would be helpful if you could use the same piece of amor/weapon but with different gem setups in different wardrobe slots; for example, this way if you want more of a certain type of gem for a boss fight, you wont need to buy two of the same piece of armor/weapon, you can just have one that has different gems in another slot.
While I understand the desire for this, it's also incredibly inconsistent with other RPGs in any RPG genre that I can think of, and a bit self-defeating. The goal is NOT to encourage less crafting. It's not an idea that I am likely to implement.
From a purely technical standpoint, there is a LOT of logic specifically built into slotting and unslotting gems. Duplicating/reusing it wouldn't necessarily be a great idea.