In my mind, these are great uses for
announce future badness. Rather than throwing out the move itself, use the opportunity to "make the world seem real" by talking about the pertinent situation and effects. So a prominent NPC goes missing - what happened to him? In conversation with Nabs it comes out: "Oh, he went up into the Fire Hills and probably got jumped by the bandits. Dremmer drove them out last spring, but in the absence of regular patrols, they've filtered back in. Someone should really do something about that."
Kapow, now you know a bunch of stuff: 1) There are bandits in the Fire Hills, 2) they can be driven off, 3) Dremmer has bigger fish to fry, 4) it's a source of annoyance/tension within the community. You don't even really need to know the mechanics behind the rule, because if you trigger it, the MC will say, "Awesome, roll +X."
The exception here is for setting-related custom moves that essentially become new basic moves, to which everyone has access. Many times they say something about the setting itself. As an example, in our hard-sci-fi AW game based on a dilapidated space station, jury rigging stuff was part of the setting. In order to eliminate the need for keeping lists of gear or tools or whatever, I just gave them the following rule:
When you rummage through your oddments to find something useful to your present situation, roll+sharp. On a 10+ you have just the thing, or near enough that it'll work more or less like you need it to. On a 7-9 you can make it work if you have to, but using it this way will be acting under fire. On a miss, you try to make it work and something goes horribly wrong in the process.
I will also give out the details of a move if it's something that everybody knows about and Harm is involved, as it is a way of
establishing the Harm. You know that a pistol does 2-Harm and you know that getting touched by a Ghost is like getting shot. This gives the players some sense of risk vs reward, which is fair. You can do the same thing fictionally (NPC shows off heinous burns on his arm and face, saying , "Yeah, it was Night Flower. They always tell you it's dangerous, but I never listened. And if someone gave me some right now, I'd eat it again in a heart-beat."), but so long as you and your players are on the same page about expectations, it's all good.