This is one of the most interesting threads I've seen in a long time. I love reading about who everyone thinks it might be and why
Wouldn't N'zoth make sense? I feel, being an old god, that would make sense. This claim was made on Reddit but refuted by others as saying the forsworn cannot be influenced by the void but what if she isn't being influenced, rather those around her are being influenced. N'zoth manipulated Vol'jin to name her warchief knowing the actions she would take, knowing the extremes she would go to. Also, as stated in the chronicle N'Zoth believed that burning Nordrassil would deal an irrecoverable blow to the world. With all that in mind, if he influenced this knowing full well Sylvanas would do that and start the war with the Alliance again in a way that would lead to more destruction and deaths thus tearing the world apart even more. On Reddit it seems the only rebuttal is that she is undead and thus can't be influenced by the void but what if this was entirely her plan and N'zoth merely had to put her on the throne and wait?Anyways, that's just my 2 cents
It was me, Dio!