I'm definitely not here to slander, especially since I really enjoyed the parts of the book you have completed thus far, and will recommend it to everyone scaling PHP once it's complete. You obviously know what you are talking about, and your writing is clear and concise. But come on, between that quote and the delays...
And to defend myself, I just checked, and have no emails from you since June 8th (yes that was a personal one from you which was appreciated), including in Spam. The only emails I've seen are from upset people asking what the deal is, via github comments. Perhaps there is some problem with the emailing system? Is there some other newsletter link I missed?
And again just to reiterate, the content of the book so far is great, and I will recommend it, however I know I am not the only upset customer.