Think about all the vanilla and TDB (and eventually HoW) legendaries that can no longer be obtained unless you happened to vault them. There needs to be either an existing vendor, or a new vendor, that sells a random assortment of those weapons once a week. Think of a used goods store or a pawn shop, except there's no actual trading; their inventory just resets every week. This would suddenly add a bunch of "new" guns and also would be easy to implement into the game.