Thanks for the new sections describing the format.  I found them very helpful.  I don't know what your alternatives look like, but I found this quite comprehensible.

> S2.5 says "the Mail Receiver MAY send a short report indicating that a report
> is available but could not be sent" - how?

This issue remains.  The text is expanded, but it still includes "the URI refers to a service that is unreachable".  A short report won't get there any better than a fully one.  I get size limits, but not that part. Consider rephrasing.

> It's not clear to me that the strict rules regarding the construction of
filenames and subjects is justified, especially when the report contains the
same information.

We discussed this and it seems to overly proscribe behaviour, beyond what interop calls for.  ¯\_(ツ)_/¯

> S3 defines a validation process that involves querying DNS at "<provider
> name>._report._dmarc.<target name>".  This will fail when this string is too
> long [...]

Discussed and I'm satisfied with the response.  However, it is definitely worth noting that owners of long domains will need to find owners of short domains to outsource to, or do it for themselves.

> The schema [...]

NEW: I completely missed that this replaces RFC 7489.  It's mentioned only in the document header and acknowledgments.  Please add notes to the abstract and consider including a section that explains the differences.