He briefly mentions the next book in the speech (quoted below) and I'm sure more will come, but the concept of mastery which is a theme in all Robert's books is the common thread between the people he interviewed

In the book that I'm writing now, I can talk about it later, if you'd like, I'm interviewing eight of the most eminent people in the world today in different fields -- In neuroscience, in architecture, in music. All of them are inherently non-conformists. All of them are inherently bucking the trend and taking their field in a completely novel direction by bringing out more of that uniqueness that I was talking about."