A surprising source for new information about the next Dan Brown novel is...Dan Brown! As part of his testimony for the ongoing court case in London (over alleged plagiarism of Holy Blood, Holy Grail), Brown submitted a very detailed witness statement which works through the writing of each of his books. Within this statement, there are a number of new clues to topics and sources for the new book. I've gone through and listed these in a new essay here on site, "Solomon Key Hints - From Dan Brown Himself". Feels good to have predicted a number of these sources correctly!