For trading, I'd like to see the item in question before entering a game, such as a picture in the game info. Or even being able to barter and trade an item in a chat would be interesting and perhaps easier. In D2, it became annoying switching characters/mules and games in order to trade a certain item because of the fact Hell characters could only see Hell games and it was typically the Hell char that needed the item that the Normal char had. Perhaps, the games could be divided between trade and playing--and in trade mode there'd be no difficulty setting. As for the currency, in D2 gold became worthless in trade, I'd like to see a better economy system.
For PvP, it'd be awesome if games being created could be sort out between this, trade, and playing. I like the idea of a rank system based upon tournaments as opposed to those who get to lvl 99 the fastest.