I mean women be taking 8-10 inches pretty commonly in porn, some VERY few at 11-12, BUT even than why does any one think beyond that is unfeasible? It feel like ego appeasement/protection. Bad dragon sells toys 14+ Inches, some with knots bigger than both my fist and you don't have to look hard to see some one bottoming out on them vigorously.
If you're put off by extremes I mean sure, but to say it can't be done when we've also got rather famous stories of women smuggling wine bottles and more (I wander if they went to the store pre-lubed).
The only thing with such scale that throws me off is it being treated as common place, or taken with no difficulty from the "uninitiated".