I'm not sure if it'll be entirely necessary since a lot of things have been redone in terms of the game system and how things work since the beginning, but since we're around Joseph's story, it could be introduced with David's story (after Moses, if we go through his life). With the whole "we want our own king now" could come a similar cry of "we want our own system".
Cogs are already the "currency" used in Aesthesia, but I also agree that there should be a new system if currency could be used to buy items and such! Bartering already happens to an extent in quests, but if we would be able to buy items, I don't think bartering should be possible.