To give a very quick update, the mithril 2 update has been merged. At this point, we're just working through reviewing the last few frontend rewrite followups (mostly small bugfixes), as well as a few small backend tweaks that we're hoping to include in this release. We know that it's been a long release, but the nature of the rewrite necessitated A LOT of review and testing. We're very hopeful about transitioning back to a regular release schedule after b14.
One thing to note is that we're always extremely appreciative of community contributions: if you're a developer and would like to see Flarum develop faster, tackling open issues, contributing to documentation, and helping with review on PRs (if within your range of expertise) is always very helpful!