I was hoping that maybe there is some book covering things like the one you described in the longest paragraph of your reply. I'm personally of opinion that such literature would benefit humanity greatly or at least that part that is doing design and programming around parts where networking meets kernels (in general, I'm also interested in non-UNIX kernels) and their internals.
Of course doing research on codebase itself is a potential way to go but I know too well from my experience years ago that it often leads to scratching your head about some parts for weeks without clear or any answer. Good literature that presents practical problems and presents different attempts on solving them has IMHO a good track record of at least decreasing amount of confusion while analyzing such systems. It also "somewhat offloads" community (developers included) from "consulting burden". As sometimes it takes even years to get answer to some technical questions.