It could be interesting to allow players to build a bank, set up an NPC banker and allow other players to come buy silver ingame, rather than over forums. The King would get a minor tax for each transaction. Also, for the risk taking bankers, we could allow for loans, interest rates and all. To get even more interesting, pay back of loans could come in the form of simple materials/goods: veggies, meat, bricks, mortar, logs, etc. Player/banker can set the acceptable payment options. Could also be used to manage WTB transactions for simple goods like those.
Very important feature: Transaction Ledgers. We need reports PLEASE.
I would love to put my Wurm silvers to work, rather than just cashing it out on PayPal.