It was a joint effort from the beginning.
Enchanting the hat was done by all four? Yes, I already tacitly agreed with you about that. But as you can see from your quotation, the Hat is still considered a relic of Godric's specifically. It is aligned with him. It is narratively imperfect for the Hat to serve individual tasks of other founders. On the other hand, Eliezer has already used it to serve a task of Salazar's, so it could do one for Rowena as well. That just doesn't fit as well. Nothing deeper than that.
Also, do you think that the crystal rod thingy is actually Gryffindor's Crystal Rod Thingy?
More likely his than anyone else's. But who knows, maybe it's Helga Hufflepuff's Crystal Rod Thingy, and then all four of them can have done something extra to the hat.
(The HPMOR discussion thread after this one is here.)
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. There haven't been any chapters recently, but it looks like there are a bunch in the pipeline and the old thread is nearing 700 comments. The latest chapter as of 7th March 2012 is Ch. 77.
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.
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: one, two, three, four, five, six, seven, eight, nine.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
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: