The new blueprint system coming in TTK pretty much guarantees they will never put a trading system in the game as you can just buy copies of every exotic you've ever found and just trade away till you have every exotic in the game within a few days.
I support the idea of trading immediately after a strike/raid or whatever has finished. You should get a chance to do it on the rewards screen.
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This this this. And never more than this, if even this.