Pretty sure its just going to be story leading into 8.2 as well as 2 higher ranking cultists/abominations or something. Maybe Lady Vashj or something similar at best.
Seem like 8.1 will be SoZ and 8.1.5 will be this 2 boss thing, probably released after blizzcon or at blizzcon or something similar to that.
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I think there might be alot more raids than usual due to the horde vs alliance theme, they can use alot of existing assets in making interesting faction themed raids alongside the entirely new and deeper story raids.