I haven't heard of any justification for why it might only take "nine people and a brain in a box in a basement".

I didn't mean to endorse that. What I was thinking when I wrote "hire the most promising AI researchers to do research in secret" was that if there are any extremely promising AI researchers who are convinced by the argument but don't want to give up their life's work, we could hire them to continue in secret just to keep the results away from the public domain. And also to activate suitable contingency plans as needed.

My thoughts on what the main effort should be is still described in Some Thoughts on Singularity Strategies.