Meta is the closest thing we have to this, but there’s a lot that happens that doesn’t get discussed here first so there’s no comprehensive source of what’s happening. We don’t map out everything we’re working on like some organizations do, so we don’t always know with certainty ourselves.
We have recently starting using an “upcoming changes” feature that is available on all recently-updated Discourse sites, and this will provide a warning and some time for bigger changes coming down the pipeline and links to a discussion here. More info on that: Upcoming Changes
There’s also a new releases.discourse.org site that presents a release timeline and when you click through to a specific version you can see highlighted changes there… for example, v2026.3.0 Changelog | Discourse Releases — this details every commit, but at this point the change has already been made… so it’s more of a heads up when you’re updating from version to version rather than a preemptive discussion, but hopefully it helps.