Right now there's 3 kinds of information we want to be distributing across moderators. One is important, not-specifically-mod-stuff, but discussions and announcements (either by Blog or Meta) that moderators should at least be aware of so they can consciously figure out "This is something our community should speak up about" or "This is something I need to at least tell the community on our own meta about". As Monica's answer points out, we're starting to announce these things to mods a lot more readily than in the past. The other is the moderator help center, also mentioned by Monica Cellio but this time in a comment - it's a bit in disrepair but we recently added a new feature to the Moderator Inbox Announcement system which will let us use site-relative linking so that new Mod Help Center articles about how tools work can actually be sent to moderators.
But the one that is most important, and is why I asked for the Moderator Inbox Announcement system to even be developed, is changes to moderator abilities / guidance. This is what the Moderator Newsletter was designed for - to be a simple, easy reference that a moderator (or anyone, even) can just look up, that is explicitly just "Mod stuff". Sure, some of this stuff is found in meta posts, and we even have collections of changes such as the Community Team feature stuffs or Recent Feature Changes, but the former doesn't necessarily cover everything mod-related that happens (some features happen because of motions not from the Community Team), while the latter covers all things. The mod newsletter was created to help focus on the stuff mods need to know, and originally designed to be able to broadcast so that mods get to know sooner.
We're looking at an in-house solution that is neither a blog (at least not, like, strictly mechanically a blog), nor is it simply making Q&A. The needs of the newsletter are simple - we need a space where we can provide basic information in a one-way communication system on new or changed mod features, with links to relevant meta discussions on the feature. It needs to be able to be linked on a feature-by-feature basis so that we can still use the Moderator Inbox Announcement system, but probably allow multiple visible on a page since unlike Q&A there's no responses present or permitted to what should be short written articles. The WordPress newsletter fell into a lack of updates in part due to some wronks in communication on new features, in part due to the fact that WordPress was overspecced for the task, and in part due to the decision made to kill our hosted WordPress instance anyway.
There may be other things we can do with the system we create for the Newsletter. Dunno yet. Still kinda in the mix as to how that's working out.