This is legit the first thing I thought of when seeing the topic title 
On the topic itself though, this is certainly a request we see come up every so often. I can understand the allure of it, I only earned the Priest and Mage sets and would love the Paladin one but I wasnât actively playing a Paladin back then so I wouldnât have really âearnedâ it if it was unlocked now.
As such, at present we still donât have any plans to retroactively grant access to all the Challenge Mode armor sets if you earned one or more of them back during Mists.