I think Blizzard really need to decide what they want items to be in this game so the design is not conflicted. Are gems objects or currencies?
In Diablo 2 for example, the intent of item design is clear and consistent. All items other than gold are represented as objects with physical properties - they exist in the world of the game. You can drop them on the ground and they occupy physical space in your inventory/stash. Gems (and by extension, jewels, runes and charms) follow the same design rule.
All objects have an appearance - both on the ground and in your inventory. In your inventory they have a picture that describes what the object looks like to your eyes. When you lift and drop them back in your inventory it makes a sound that tells your ears it is made of some material property that a similar real world object might have. A gem makes a resonant, pinging/chiming sound.
But when we get to Diablo 4, its not clear at times if Blizzard wants items to be objects or currencies and sometimes they are both at the same time. A rare armour drop is both an object that you can wear and a currency (veiled crystals) that you can salvage into. You salvage items into a currency because the item is garbage. And thats a problem because you need the currency to do stuff like upgrade, so you are incentivised to pick up unbelievable amounts of garbage. This is why you have no inventory space.
I generally dislike currencies because they are represented solely as a number that goes up in some UI tab and you don’t get a sense of currencies as being real, material things. Looting them doesn’t feel as satisfying. They are just numbers that go up and a certain amount of that currency is subtracted when you want to do something like enchant. Diablo 4 already has a lot of currencies - much more than physical objects in the game world.
The reason why one would want to make gems a currency is to free up inventory space. Inventory space is desperately limited but not because of gems. It is limited because of aspects and bases for imprinting aspects (rare items).
Half of my stash and mule space is filled with legendary items with perfectly rolled aspects that I am either saving for when my best in slot items drop or they are saved for other characters (when they level up enough to use them). The other half is filled with high item power rares that I want to enchant but don’t have the gold to do it yet.
Why do I keep the legendary in my stash instead of extracting the aspect? Because transferring aspects between mules is more limited than transferring legendaries. My level 1 mules do not have access to the enchanter. They do have access to my shared stash. Furthermore, there is more inventory space available to store legendaries than there is to store aspects. So I only extract the aspect when I’m about to imprint it.
I feel like turning gems into a currency is like trying to treat a broken foot with cough medicine. It isn’t solving the root cause of why you don’t have any inventory space. Whatever space you get back from turning gems into a currency like veiled crystals will be filled back up with legendaries in less than 1 day.
And by treating this as a solution, you are removing another physical object from the world. There are already so few types of physical object in it - only rares and legendaries really.
But if they want to make everything except wearables into a currency then do it, but make the design coherent. Do it one way or the other way, but not this half way thing we have right now.