This is why they won't be coming until 8.3.5. They don't have a story reason to join until after every casual has beaten LFR Nya'lotha and killed Ra'den, so they will have until 8.3.5 to work on their models and implement them as playable. They won't release Mogu without a pair, just like they waited THREE PATCHES to implement Vulpera (because they needed to reveal Mechagnomes), and that pair AR exists as Ankoan that they are likely working on behind the scenes: the models are already more developed than Kelfin.