Reforging is a bad idea for all legendaries, which is why it was removed after House of Wolves. In case you weren't playing back then, being able to reforge all legendary items quickly led to the vast majority of players spending materials to reforge their gear until they got a perfect perk set. Which meant that (especially in Crucible), everyone was using the same guns with the same perk rolls and variety and diversity went out the window. It was a bad idea in the beginning and I doubt we'll ever see it return for legendaries.