Too complex for a medieval society.
false.
http://en.wikipedia.org/wiki/History_of_bankinghere's an idea. why wait for the devs to develop and implement a banking system? why not develop it yourself in game? create a character who gives out loans to other players, and have them pay you back with interest. they don't pay you back? break their legs.
also let other players deposit their tria with you, where it can earn interest. they can make deposits and withdrawals at will.
here's the thing folks. in RL, people don't just sit around with a novel idea and say, "oh boy, I sure do wish this would be developed and implemented, because it's a really good idea. boy, somebody should really do it."
no, they get off their butts and do it themselves. your characters should have the same motivation and initiative that they would in RL.
i've said it once, and i'll say it a thousand times more, this game would be infinitely better without NPCs. quests are pointless. we should be able to train each other. institutions such as governments, merchants, banks, whatever should be RPd by players, not controlled by scripts.
my two cents. with compound interest.