Account bound Currency ... and a trade market to trade with other players

Full multi player may never be an option but a trade market could be a cool thing to have to buy and sell resources.
Have an account bound currency that is linked to an account and not a single game.
Allow people to buy and sell and get stuff delivered via cargo ships.
Could be done like that or to add an extra feeling of not being alone have a cargo ship arrive on both the buyer and sellers game to show the transaction.