The issue of changing the content model for the "N" property in the vCard XML DTD is a difficult one. True, that the semantics seem odd for allowing multiple family name. However, this is the standard specified by RFC2426. The last thing we want is to have two RFCs specifying what the vCard standard is. Hence, rather than correcting the vCard specification within the XML DTD, we should be submitting change requests to the vCard standard and reflecting the changes, once accepted, in the vCard XML DTD.
We can certainly provide a comment in the DTD that reflects the semantic clarification.
-- Frank