Typically at the end of an expansion we see tests for later expansion technology or models, for instance the new Garrosh model in WotLK, which inspired the Pandaren model in MoP, which inspired the newer Garrosh at the end of MoP, which inspired the new race models in WoD. At the end of WoD we had new demon models for Legion.
So it's interesting to speculate what Argus means for the new Xpac, they've created 3 new zones in Argus, with a range of new models and not just using sporebats. Such as the Broken and the Void-Broken that are a lot like Pale Orcs (void devolved Orcs), the Ethereals, the new space panthers, etc. Does this mean that not just Etherals like Locus Walker might be involved in the next expansion, but Broken/Void Broken as well?
My speculation on this means that there's a slight likelihood that Argus either becomes a 1-20 newbie zone for a new Ethereal race in the next expansion (who have to clean out the remaining fel/void remnants in Mac'aree) or that a large population of survivors get relocated onto Azeroth, including the Krokul faction of Broken who assist us in fighting the void on Azeroth.