Sylvannas divided Soul

In A Good War, while the Horde was still in Astranaar in Ashenvale, before even making it to Darkshore, Robert Brooks had Sylvanas reveal an internal monologue:

    The kaldorei knew they were outnumbered. They knew their homeland was lost. Maybe a few of them knew in their hearts—just as she knew—that Darnassus would one day burn to ashes.

Before even fighting Malfurion for the final time, and before realizing that she had walked away like a James Bond villain without making sure Malfurion had been killed, Robert Brooks had already let us know that Sylvanas was intending to burn Teldrassil.

In addition, Robert Brooks again foreshadowed that Sylvanas had a secret true objection that she was only using the Horde for, goals that Elune and forces that we only end up meeting in Shadowlands opposed. Effectively, Robert Brooks wrote into A Good War how Sylvanas had intended to burn Teldrassil all along, and she was only forced to have it done out in the open rather than whatever quieter way she was going to have it done while dragging out her war to kill as many people as possible:

    And that was almost certainly true, wasn’t it? Elune had intervened. Perhaps she had even stayed Saurfang’s killing blow. And she wouldn’t be the only force beyond the Alliance to oppose Sylvanas’s true objective.

    Sylvanas’s anger grew cold.

    She had known this would happen. It had simply come sooner than expected. That was all.

Robert Brooks’ subtle writing went over the heads of a lot of people because it was written in such a way that doesn’t make any sense without context that wasn’t revealed until more than a year later at the Blizzcon Shadowlands announcement.