Such a terrific book. How outdated do you think it is now?
For starters, server push turned out to be very hard to use effectively, and in some situations could make things worse. It's been deprecated for awhile now, and last year Chrome effectively disabled it by always sending SETTINGS_ENABLE_PUSH = 0, which tells servers not to use it.
The HTTP/2 prioritization scheme was partly deprecated in RFC 9113. The browsers all have different interpretations, and Safari/Edge effectively don't use it. On top of that, many servers have TCP buffers that are too large to allow priority changes to work in time. RFC 9218 introduced simpler prioritization headers for HTTP/3, and it's been suggested as a backwards-compatible replacement for HTTP/2.
That's just in my area of expertise. There's probably more. It looks like a good book, but it seems it hasn't been updated in the decade since publishing.
Some links:
https://jakearchibald.com/2017/h2-push-tougher-than-i-though...
https://developer.chrome.com/blog/removing-push/
https://chromestatus.com/feature/6302414934114304
https://datatracker.ietf.org/doc/html/rfc9218
https://calendar.perfplanet.com/2022/http-3-prioritization-d...
https://blog.cloudflare.com/better-http-2-prioritization-for...