WoW's focus from here on out needs to be subscriber retention and engaging its players. The two go hand in hand, and the more Blizzard can do to involve the community, the better. These Summer Challenges are a great way to give a little structure to an otherwise unstructured experience.
Blizzard has even included links to Wowhead's excellent transmog set viewer so you know what drops you're looking for. It's good to see Blizzard recognizing Perculia's hard work.
Blizzard's full announcement is below.