It's a joke, yes. MoR has been known to be hilarious at time, although not so much recently.
Given Eliezer's commitment to truth, however, I'd say there's about a 30% chance he was telling the explicit truth, though I wouldn't think she'll stay that way.
The plot of HPMOR was planned from the start and Eliezer started writing it before FiM premiered. What reason would he have back then to consider putting horned, winged horses into the story? And I think that if Hermione does return, it won't be in a way allowing for some sort of cross-fandom referential side-joke added as an afterthought. I wouldn't give it 30%.
Which is all a great shame, because everything is better with ponies. ;)
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 93. The previous thread has passed 300 comments.
There is now 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.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18,19,20.
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: