Meghan Hicks could do it, only woman to finish Nolan's under the cutoff. Everyone always talks about how Barkley is the hardest 'race' but it really isn't a competitive event. Nolan's seems harder, no idea how many have attempted it but it is open to literally anyone and around the same amount of finishers as Barkley. Whereas Barkley with its convoluted entry process and very small field of runners, it will never be a competitive event and that is not what Laz is going for anyway.
I think a lot of it is appeal. The Barkley is really only appealing to a very niche group of people within a niche sport. Sure it has reached the masses now as far as awareness goes, but I have a hard time thinking even half of people who run ultra's ever actually want to run Barkley. Speaking as an ultra runner myself I have almost no desire to ever line up at that race. Theres so many other races I'd rather do than Barkley.