Anduin has been portrayed as the perfect protagonist in recent times, almost too perfect. What if this almost too perfect demeanor is to conceal the fact that it is in fact Azshara behind the veil? This would be the big Azshara twist we didn't see coming.
Sylvanas has known this all along with the Xal'anath whispers and is why she has been pushing hard to defeat the Alliance, when it is in fact Azshara that she is after. Defeating this major threat is the only way she feels she could save Anduin, the Horde and Azeroth from the even bigger imminent threats. BFA is hence all about Sylvanas' battle FOR Azeroth. This is why she has bolstered her undead numbers. This is why the devs keep on insisting that she is in fact morally grey, as she has to make difficult decisions for the greater good.
Sylvanas hasn't disclosed this to anyone due to fears that no one would believe her and that other Horde leaders might think she's crazy, and cause greater civil unrest which is exactly what Azshara wants. As a result of her actions, Sylvanas will not be trialled in chains or sentenced but will continue to lead the Horde as Warchief and command both the Alliance and Horde through the battle of the old gods.