I'm against straight up trading but it would be nice if you could divy up the spoils of a raid. Like if someone gets their 10th Gjallahorn but someone in the raid party has never gotten it, you could give it to them.
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Diablo 3-esque trading system would be great. You can only trade top tier items for 2 hours after you get it, and only with those who were in your fireteam when you got it.