1) No one has jumped to the "wrong" conclusion simply because Vol'jin AS Warchief and Vol'Jin NOT AS Warchief are both plausible ideas until Blizzard actually names the new Warchief
2) Unrelated subject matter? Blizzard has said many times the books and such outside of the online game add to the story and are intertwined with the lore of the online game so I wouldn't go so far as to say that a book about Vol'jin is unrelated.
3) As for losing the point of what the story is about (Orcs vs Humans), again it's Blizzards game and they can change it how they want at any time without your approval or consent. Blizzard has proven this in the past buy "adding" lore or "ignoring" lore (other ppls words hence the quotes) as they see fit.
On my own personal note, I like the idea of a non-orc Warchief I'm just not sure its gonna happen