I'm running Normal difficulty for one of the challenges now. I just noticed what looked like set rewards after one of the runs. It was one Hellfire soul plus an Echo talisman, consistent with what we would have seen after passing Normal the first time in prior dungeons. So, maybe it's fixed now. And maybe we'll get them after passing each difficulty, as in the past.
Update: I just ran Hard and got set rewards there, too. Looks like it's fixed.