I would estimate a probability <3% that the author is Alicorn; we talk on AIM often enough that I think I would have noticed the familiarity of her style if she had written it.

Having read the article before reading this comment, I developed the distinct impression that I was reading another of Yvain's posts partway through. I would estimate 45% confidence that the author is Yvain, and 50% confidence that the author is someone else whose writing style I am not familiar with, so not Alicorn or Eliezer.