The release notes for the next release typically get started about 10s after current one has been uploaded. Usually with merely the version number changed, hoping that subsequent changes get updated as they happen - because writing release notes is hard, often harder than doing the release itself (especially for the demographic that likes development, but not necessarily writing prose), anything that eases that burden and distributes that over time is helpful.
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Disclaimer: I'm not an OpenWrt developer, but I've been in those shoes often enough - and I've done it always like that (only that my in-progress drafts were maintained locally and not visible to the public).
I hope for a release soon, it looks like all the fixes mentioned on the release notes page have been merged into openwrt-19.07 and all but one of the release goals mentioned here: https://openwrt.org/docs/guide-developer/releases/goals/19.07.4 have been fixed as well.
Some work had resumed on the 19.07 tree shortly after I had posted this thread so that is also a good sign.