Ten years hard?
A GW2 style system for crafting mats would be the single best QoL imaginable for the game
They would lose some money on retainers, but I think most people that have 4+ retainers would still keep extra because retainers are useful for more than storage
Yeah, I already said why I think they don't do it. It might be difficult, but in the long run it's the best for the game. Yoshi-P said he wants to work in the game for another 10 years. Does that mean he wants a broken code for 20 years? Cool.
So much for being civilised. Reasoning seems impossible with this one.
While it does make sense that they'd probably be hesitant to add another free retainer and instantly wipe off that much money they are currently earning, they are adding some amount of ancillary inventory in the form of extra glamour dresser slots. If they do give us an additional 400 slots in 6.2 as they previously indicated they would, that's going to be more than two retainers' worth of inventory space that can be cleared out.
Youre assuming that crafting items could go into another place and somehow be treated more efficiently than standard inventory, but I don't think it's possible.
The closest thing we have to what you're asking for is the armoury chest, but it's not any more efficient at storing things, and also if you need to craft something with a gear piece as an ingredient then it has to be in your main inventory. It's like the crafting ingredient menu can't see it if it's in the armoury chest.
From what they've said in the past about the unfeasibility of a tackle box, I don't think it could store things any more efficiently than main inventory – still one slot per item, with a limit on how many things can go in, except now those slots are walled off to only hold one type of item instead of general-purpose slots with the same degree of being accessed anywhere.
As I wrote earlier, the quest item "inventory" is an illusion and the items just appear there when the relevant quest is active. You can't actually put items in those illusory slots.
You'd be surprised, inventory databases often sit at the bottom of a giant pyramid of code in MMOs; look at the headaches the backpack system gave the devs over in WoW, they spent two decades trying to upgrade it to no success and had to go through all sorts of mad smoke and mirrors to roundabout their own programming to give players more bag-space. It seems simple because you know, "iTs JuSt FiElDs In A dAtAbAse!11!", but it is often the hardest most entangled part of the whole game.