WL7 needed something because there wasn’t even an decent pdf. As a matter of fact, the absence of a decent manual was the #1 reason for hating WL7. Maybe thats why a 3rd party finally jumped at the opportunity?
WL8 has a great pdf. Do you think a 3rd party could improve it? I think the pdf is pretty comprehensive.
I too would like a WL8 book and would pay extra for it. But these days I think I’m in the minority. Besides rabid environmentalists will always explain to me why I don’t need a physical manual.