I loved the DW guide. It's been super useful for myself, as the DM, and for my new players. I do have one thing that we've all struggled a little bit with that might be worth adding in: fictional positioning. It's a little difficult to wrap your head around at first, especially since so many RPGs rely on non-fictional/mechanical tools to create the context in which things interact. For some things it's easy to see how it works, like the example of Smaug/the dragon in the DW text, but other things are a little harder to relate and conceptualize starting out.
For example, I'm running my group through the Bloodstone Idol adventure to start and they attacked the Demon Urlaz rather than talk (notably the Paladin's doing there). They started attacking, and mostly missed at first, until the wizard burst through with magic and took it down nearly by half. It was then that I realized a bunch of adventurers with no magical tools, or real effort were going to take down a (low-level) demon, and I started to think better of it. Following the wizard people started to actually hit, but armor applied and caused less damage. I increased the demon's armor so that it wasn't dying that fast, but in hindsight they shouldn't really have been allowed to roll hack&slash/volley in the first place.
I guess my own confusion in this is how to relate fictional positioning to players when they can literally walk up and touch the demon (as opposed to the flying dragon). There's always the whole: it has lots of armor and mundane weapons won't ever harm it schtick, but after a a few monsters like that it seems like it would get old. I'd personally like a little discussion on how fictional positioning can be better used. It should be useful to both GMs and players since it'll give a GM tools and ideas, and give players an understanding of why they can't just walk up and beatstick the demon in front of them.
Just my 2 cents on it. I've really enjoyed your work and the effort you've put into it. Thanks again.