In my previous life as a Support manager for a global software publisher, that would have MANDATED a study on the effects and a UAT before deployment to the production branch
IMHO that is comparing apples and bananas. One the one hand a global software publisher with a full-time paid team and here an open-source project mostly driven by spare-time devs (very few at that when looking at the frontend specifically).
I get the point that this was a somewhat disruptive move and in the future might be handled differently, but you already mentioned the “pain” that trying to support various additional different parallel implementations (via different config checkboxes) would introduce and the maintenance burden that always comes with those.
Reg. more upfront communication (also mentioned by @maxym): Who should handle that? The already limited devs? Not really realistic for the project currently as far as I see it.
Looking at it from my purely personal point of view as an frontend developer in this project: I am already investing my spare time to e.g. fix frontend bugs (mostly ones that do not even impact my HA setup). I cannot see myself on top writing blog posts or forum posts about upcoming changes / fixes. Then many things would simply not get changed / fixed anymore.
Also the release notes are available a week before a new release in a draft version once the beta hits, so then people not following the development process, can already get a heads-up.
Once again, I understand where you are coming from, but I fear there is a lot of wishful thinking in that comparison.