No plans to do so right now, and if I ever do, it would be a very different kind of book than the first. In that book I put pretty much all I have to say to a general audience, and not much has changed over the past decade since it was written.
A book that doesn’t seem to exist that I’d like to work on would be something along the lines an advanced undergraduate to graduate level textbook on topics in mathematics and quantum theory. Maybe someday I’ll find time and opportunity to start that project, but not this semester…
Update, summer 2013: I have been writing a book on quantum mechanics from the point of view of representation theory, the latest version is here.
Update: The new book will be published by Springer, publication date is December 2017.
Update: The book has been published, see here.