There are several cleanups and improvements that would be nice to get into a revised .changes format:
Bump Format version to 2.0. (Probably support generating both format 1.8 and 2.0 from dpkg-genchanges for a while to ease the transition.)
Fix the Binary and Description fields to only list binary packages currently being uploaded (818618).
Get rid of the Files difference compared to the other Checksums-* fields and the Files field in .dsc files. By:
Using a Checksums-Md5 field instead of Files, without section and priority values.
Removing the md5sums digests from the Files field and moving the filename to the front of the entry. Renaming the field to avoid confusion with the one in the .dsc file. Perhaps name it Artifacts?
Add a new Checksums-Sha512 field?
The Distribution field contains information about what is commonly referred to as a suite. Rename?
Clarify the Changed-by and Maintainer fields?
Changed-by is intended to be used to list the responsible entity for the changes to the source for this upload. It gets its value from the email address in the latest changelog entry. On maintainer and NMUs it lists the person that prepared the release. On binNMUs it lists the buildd, which does not change the source except for adding an entry to the changelog. A better name could be Released-By, for example?
Maintainer is intended to be used to list the responsible entity for the artifacts built for this upload. It is used to receive mails from archive software. On a maintainer or NMU upload, it lists the value from the debian/control Maintainer field. On an upload by a buildd, it uses the buildd address. A better name could be Built-By, for example.