Before the split between Moby and Docker, pull requests were automatically assigned to the current (work in progress) milestone for the upcoming release.
Pull requests worth mentioning in the actual changelog were labeled with "impact/changelog", and during the Docker release, the "release captain" would go through all PR's on the milestone labeled with "impact/changelog" to write the change log for the release.
Moby no longer does releases (the "tool" may at some point), and keeping track of changes for downstream projects (such as Docker) is not a responsibility of the Moby project. This complicates things for Docker, as it's not as easy to tell which Docker release a change ended up in.
I'm proposing to create a weekly change log, collecting all pull-request that were merged with label "impact/changelog". If we think it's worth doing; perhaps include all pull requests (under a caption "other changes")
Downstream projects can use this change log as a reference for their own changelog.