Just to cut out the RNG on RNG. Getting a Legendary should be a good feeling, not a bad one (like getting Sephuz or Prydaz). Would it be a bad thing if you can just trade a legendary for a one you do like? Price could be an X amount of Blood of Sargeras or a few Curious Coins. Now if everyone trades his Sephuz and Prydaz for another legendary that is the developers mistake of making such underwhelming legendaries.
I'm also extremely surprised they are adding a legendary upgrade item into the game once Nighhold releases. Rewarding lucky players with BiS legendaries even more