Many major printers now require this format for PDF book cover files. Many authors and self publishers buy Adobe Distiller just to fulfill this requirement.
Changing to an enhancement request. The biggest problem is that this standard does not support RGB nor any of the CIE spaces, so RGB colours need to be converted to CMYK or gray. There is no provision for this in pdfwrite at present, normally we set -dUseCIEColor to convert the colours to CIE and then embed relevant CIE/ICC colour spaces. The remaining features/restrictions are already in place.
*** Bug 694359 has been marked as a duplicate of this bug. ***
Fixed in commit be998e2366e8c48d72602672a6d4357b90a77a50 Please read the commit log for details.