The Trading API should allow trading between characters, or at least smoothen the process of trading between characters, as currently you will have to move the items to each player, trade, and then move them back to the character.
It should also provide information about the new instanceIDs of items generated in the trade. This exacerbates the character trading issue because there is no way to track what the newly created item instance IDs are for transferring back to a character.
It should also provide better monitoring support for ongoing trades. The current TradeStatus stuff is good but it requires you to send the tradeID from one player to another, this seems not very secure. Could there be a call for getting all trades related to a player, whether they opened or accepted it?