I feel it could be done if we limit what could be traded, similar to what you said with the materials. Just allow vendor gear and materials to be traded, because I find it to be a huge pain to farm for saphire wire on my hunter when I mainly play warlocks. I also know quite a few people who would gladly exchange a good rolled legendary shotgun for my light/beware. If they ever do allow exotics to be traded, (personally I dont think they should even though i would do literally anything for praxic or a g-horn) they should make it where equipment soulbinds whenever you equip it- which makes it unable to be traded. I also think bungie should impliment a system where only items of equivilant value could be traded. How they would determine which exotic is equal to another is beyond me. but this is just my 2 cents, and my thoughts on it.