Please, Bungie, never add a public chat or trading into this game. Trading may be acceptable if it's inventive and very limited somehow. I don't want to hear/see everyone else's crap flooding my screen. It would take away from the air that the game has. Also, I love claiming my items and gear as my own- ones that I've unlocked and found
Some form of chat or in game communication method is needed other than the limited fire team chat. As for trading the only logical method of trading I could see implemented is a timed trade window for drops only to those who were present when the item was picked up.