I don't think that one would actually be revising the core CIF definition in any way, just allowing the mmCIF definition to cover a case which is exactly parallel to the small molecule definition, by taking the entity definitions as the functional equivalents of formulae. The macromolecular case is fuzzier than the small molecule case, but the PDB Z happens to match the wording of the _cell.formula_units_Z if one adds entity definitions as formulae.