OK, thanks for bearing with us while we fleshed this idea out. Here’s what we’ve come up with:
From the #feature:announcements post:
While we have always posted detailed release notes for major version along with a blog post highlighting major features, we don’t generally talk about our 10+ beta releases leading up to the major release. After hearing feedback from members of our community, we’ve decided to try something new moving forward. We’re going to share release notes for each beta. They’ll feature the beta’s “Greatest Hits” - explanations of new changes that we think everyone should know - as well as a list of smaller changes that don’t need quite so much detail.
We didn’t feel like a weekly update made sense. Development is not “constant”, we don’t use weeks as a deadline/timeframe, so weekly updates do not reflect our development cycle. We release a new beta when we have something new to share that is stable for sites to update. The last thing we want to do is share an update about a new in-progress feature and then have everyone update only to find it’s not fully ready yet.
We plan to try these release notes out for a few betas and see how they go. Let us know what you think about them here.
I actually posted the release notes a few hours ago, but messed up security permissions on the category so only the team could see it 
Also, we’ve decided to restrict replying in the #feature:announcements category, just like we do in the releases category. We don’t want to split discussion about a feature into multiple places, so feature discussion will continue in feature, #feature:announcements will be reserved solely for the announcement itself. Bugs for new features should be reported in a new bug topic, unless we have a “help us test xyz” topic linked.