This is why it should be a mod and not in game by default. This dramatically changes the use case of a trader and just turns them into a quest giver for the majority of players. I don't see myself using them for bartering if this is implemented in the way you describe. The amount of storage we would need would QUICKLY get out of hand. If you want to play apocalyptic hoarder simulator, this is how you'd do it.
I like the idea, but it's too far from the original intent of the trader in my opinion.