I really don't know what to say, Jellby.
The discussion is entering the realm what is more important, a purist approach to follow the standard "to the letter", or creation of ePub file that works on real implementations of the said standard. I personally don't understand the technical reason why the standard is enforcing, and so strongly, the value of "8". I am also unaware of the implementation that does not accept value "9".
The question is, should the epubcheck and flightcrew be updated, or should we petition the
IDPF to accept the experiences of the actual implementation relaxing the requirement in the process?