Wonder trading could only work if every weapon/piece of armor went into the same pool. Dropping in an exotic should not guarantee you an exotic in return. Otherwise, people would keep doing it until they got gjallarhorn essentially. This also probably wouldn't work though, because no one would put in an exotic knowing they weren't guaranteed one in return. In my opinion, wonder trading wouldn't work.

But it would be for like, excess armor and weapons. If you got you're sixth ghorn from the nightfall then instead of getting your 10th exotic shard you could send it to someone else