I didn't see this formalization used on LW or the wiki, perhaps it is of interest.
https://encrypted.google.com/search?num=100&q=Kullback-Leibler%20OR%20surprisal%20site%3Alesswrong.com
Speaking of the LW wiki, how fundamental is it to LW compared to the sequences, discussion threads, Main articles, hpmor, etc?
Not very, unfortunately.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.