In adding Edm.Primitive as a type specifying "any primitive type" we introduced a problem for JSON. We have no way to annotate individual elements of a JSON array, so we have no way of specifying the types of a heterogeneous collection of primitive types. In some cases these might be heuristically determined, but not all. We might consider disallowing collections of Edm.Primitive as being underspecified. In the future it would be non-breaking to add these as long as we solved the primitive types in a json array problem.