Earlier quoted context omitted.
It's kinda weird to think of brain as an X project. DistBelief was developed out in the open in the main source code repo by people you think of as googlers, like Jeff. So what makes it "X"?
A need to justify X's existence?
My own personal image of X was that if you had to drive to some old Air Force base to see it, it was X. Since brain was software, it doesn’t fit the model.