A craft inventory system like Elder Scrolls Online with an endless crafting mat inventory separate from regular inventory where, while crafting, it reads and takes from the craft inventory. Half the system for this is already in game with the current Gear Armory and Shard/ Crystal inventory that puts items in a separate inventory instead of normal one. Just make one for crafting mats and make it endless or at least the current 9999 stack that shards and crystals go to. Instead of using icons and individual slots like the regular inventory and armory, just do it as a list view with crafting mats in alphabetical order with a search field, incase you want to retrieve the items to put on a retainer for Market Board sale. You could also have quest that require crafting mat turn ins take from this crafting inventory.

Another idea would be to simply make crafting mats that are in chocobo saddlebags and in retainer inventory usable by the crafting interface instead of having to constantly search each of those inventories to retrieve items to the normal inventory before you can use the items for crafting. It is also a major inconvenience having to keep running from a crafting area to a summoning bell to get items from a retainer.

Either one of these ideas would be a drastic improvement to the quality of life where it pertains to crafting. There are just so many different mats in the game and every one also has a high quality version, that it takes up a ton of storage just for crafting mats alone. This would also get rid of the headache of constantly running to a summon bell to access retainer inventory and searching through pages of inventory for a few items you need to craft something.