I don’t know the world of archives and dumps, but I wonder if there no existing standard (either de facto standard either a true standard) for our dumps. Perhaps some of the following compagnies/institutions have interesting standards that could fit our needs: MySQL, communities dealing with SQL dialects, archive.org, digital archives (Europeana, American archives, etc.), archive softwares (Bacula, etc.), Kiwix/OpenZIM, Drupal, etc.
Also it is probably simpler creating a special dump/archive type, a quick overview of existing archive types could orient some choices if we want move in some years to some standard archive type. I am thinking about that because I heard the longevity of the archive type is a true problem (difficulty of read archives created some dozens of years ago); although you are here only dealing with dumps (short-life archives).