This would be incredibly helpful. For crafting components, we'd know when we got up to the total number we need. For gear, we'd know if we already have an item and shouldn't buy or waste a quest reward choice on getting another, etc.

I don't expect it's likely to include the retainers' inventories, though, since the whole point of storing items with retainers rather than just having that much more inventory space ourselves is to reduce the load of what info the servers need to keep constantly maintaining. The game servers don't know what our retainers are holding except when we go to a summoning bell and retrieve that info from the database. It's not going to go through that database download every time it needs to show an item tooltip.

But still, even without the retainers' inventories being involved, seeing the total number of such items that we have on hand rather than just the number of NQ ones we have would be a huge improvement.