I didn't get that from the article: I understood the idea to be to use the existing implementations of the urgent pointer, in context of the BSDish socket APIs

I didn't get that from the article: I understood the idea to be to use the existing implementations of the urgent pointer, in context of the BSDish socket APIs we have, as message boundary markers. And, if that is done, we end up in the mess that RFC 6093 clearly describes.