| Because idref is only defined relative to its enclosing document,
| this means that it's remarkably difficult to create a reference
| to remote entities, meaning that any NIEM document effectively
| has to contain the entire serialization of all of its objects.

I'm not sure I follow this.  IDREF is far from a general purpose
reference mechanism.  It's for intra-document cross-referencing only.
(See the FPML specs for reasonable use.)

Too much water has flowed under too many bridges to bring up the
dreaded H-word again, so I'll let it go at that.