The amount of feedback you can provide for "format behavior" is pretty limited because we don't have any types that require ISO/IEC 60559 behavior. is_iec559 only imposes requirements on the representable, not on whether e.g. certain calculations are correctly rounded or infinities and NaNs are propagated and produced by operations. Similarly, C's _Float32 and other interchange floating types don't imply Annex F conformance, and the C wording is very clear about that.

There is flexibility, but you can still classify a format as generally being an ISO/IEC 60559 binary interchange format, which at least tells you that infinities and NaNs are present and that the format represents values in the same way, even though with different amount of exponent or mantissa bits. I think both having a quick and reliable way to classify a format as binary32 and having a way to query information about floating-point representations in general are necessary.