Similar to the one GA people get for collections - I think it'd be a lot easier for people who want to put anything new they may have gotten through quests (which will, given the nature of quests, be in amongst a large pile of other stuff) into their wardrobe, as it'll show exactly what went into the wardrobe as well as only try to put in actual clothing instead of wasting time trying to put non-clothing items in like quickstocking does. It could go on the wardrobe items page next to the remove button, in theory; it seems like a logical place.

Quickstock does exactly that though. It could stand to be cleaned up because like you said, it's silly that it gives an error for every non-clothing item in your inventory. But quickstock is exactly what you're asking for here, and it exists.

Except it isn't. See, quickstock just for filling a wardrobe still requires choosing a shop even though it'll just be going to the wardrobe, and it doesn't tell you what actually went into the wardrobe - just what didn't - so when dealing with a large amount of quest items or vends it's very difficult to see what new things have been obtained. I agree it's useful, but it could be improved.

With the newest wardrobe page here you can select the timeline and see what you've added (or in your wardrobe itself, you can select "added to wardrobe") There could be a total removal of the message stating what hasn't been added, but I don't see the use for another feature like that.

Between quick stock, and viewing the "added to wardrobe" section, I see no need for this.