So I started playing Diablo 3 again recently and got into the Necromancer lore. The stuff about Trag'oul (his Ourborous like form and his relationship to maintaining the balance) is very similar to what we are seeing with Oribos.
This is not to say that the worlds that Trag'oul left for are warcraft in some sort of HotS crossover antics (though it could be fun) but just that Blizz like reusing motifs and ideas from their other games (like the Void Lord thing in that Starcraft manga), with the obvious previous Diablo similarity with Waracrft being soulstones.
So could this give us hints of what we could expect? In Diablo Trag'oul is the brother to Tathamet (the 7 headed dragon that the 7 evils spawned from, and unrelated but in itself is similar to Y'Shaarj) and was born at the start of creation. He is also obsessed with balance itself and not particularly siding with good or evil. Which could give us hints that what the Arbiter wants, as what it wants may not be what we want.