I suspect I'm spoiling the in-joke here, but is that a literal in-story thing, or just a fan joke? Honestly, it's getting hard to tell sometimes.
It has to deal with an author's note written after Hermione's death, in which Eliezer responded to claims that the story was insufficiently feminist with 'wait until the story is finished!', and ended with the line that she would be resurrected as an alicorn princess. It was, I believe, at the same time that the MLP community was still reacting to Twilight Sparkle being turned from a unicorn to an alicorn princess.
People have been genuinely uncertain how serious he was, given his reputation for both honesty and silliness.
And when the similarly themed, similarly silly suggestion came true that Twilight Sparkle (in a pre-alicorn state, as it happens) would appear in the fic, people really began to take it seriously.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 111.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: