What are they about? Essentially, optimizing your HTTP responses for the ways in which actual web browsers make HTTP requests. Any web performance analysis tool worth using (like YSlow and PageSpeed – both of which Steve Souders was involved in btw) recommended the practices outlined in those books.
So, no. I don't think a new book with updated practices says anything about the protocol. The optimization tips from this book will simply become widespread common knowledge the same way they did in the past.
[1] http://shop.oreilly.com/product/9780596529307.do [2] http://shop.oreilly.com/product/9780596522315.do
That book is also a phenomenal resource on the performance of all things web-related, so you should check it out regardless of any concerns you have about HTTP/2.