This would only work if GitHub Pages had a post-render hook, that is, fire off a hook when it's done rendering a page. Not a post-commit webhook, but a post Jekyll-render hook. Ideally it would include front matter (such as the permalink) so I could do stuff based on the ID I give it. For example, my Just a Gwai Lo: Questions blog has the ID of the tweet I reference in each post. I'd love to have it add an automatic reply to that specific tweet with a link back to the comments page so that people could comment at more length.