I have seen bigger prints than that made from 35mm from great scanners. Optically it would be difficult but doable. In general when I read something can't be done I usually think the person stating it doesn't know how, so assumes it can't be done, or believes all the crap that is written on the internet. To say that a large negative is needed for a large print is completely ignoring the most important aspect of any image which is the content. I once saw one of Capa's D-Day images printed to 8 feet or so. Still amazing!