It's not very useful measure.
So, there is Lesath Lestrange, an original character. Which is more likely: "Lesath thinks that Harry is his Lord" or "Lesath is a 3-level (or any specific number instead of "3") player who wants to decieve Harry, and also he is H&C which is possible because he knows how to fool anti-obliviation wards"?
Your approach will just say "I don't know what to make of it. We have already departured from the canon and I can't work here" with a sad look on face.
EDIT: I re-read my comment, and it seems to be arrogant and condescending. I didn't intend it to be so, and not sure how I should change it, so I figured I should just apologize beforehand. Your approach to assigning priors is reasonable one, it just lacking some vital parts.
I agree that it's an incomplete measure. As you point out, we would need some measure of the complexity of divergences from Canon, which requires a more general measure.
Another way to put it would be, I don't think it's unreasonable in a fanfic to assign all the details prescribed in Canon a complexity of zero.
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 96. The previous thread is at almost 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, 21, 22, 23, 24, .
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: