Contributors have already raised very relevant issues of competitors' interest levels, marshalling, cost, and increased traffic. It occurs to me however that there are other relevant issues, two of which are related - professional marketing and sponsorship and public appreciation of ultra running.
Before commenting further on this it is very interesting to look back to say the 1880s - the days when the public went beserk to see ultra runners in their colourful costumes, Days when George Noremac dominated events of up to six days duration and earned a fortune in prize money along the way. Days of professional athletics, a period which has of course now returned even stronger. But alas such has not embraced the sport of ultra running.
Can a fringe sport secure major sponsorship, secure the interest of television companies, and have its profile significantly increased?
The answer is most certainly "Yes." Whilst I cannot personally provide 'nuts and bolts' advice as to how such is achieved I am proud to compete in the fringe sport of longdrive golf. A sport which was until recently barely surviving in Europe but is now almost overnight fifty times stronger thanks to professional organisers (backed by great sponsors) coming on board. So, at 62 years of age, I now occasionally appear on tv in the European Senior Championships. Incredible as my main love - ultra running - died over 40 years earlier due to injury. The only sport I thought that I could ever be successful in.
I still love athletics far more than golf, but nowadays only as a spectator. I would love to see ultra running secure the boost which my new sport has. Irregardless I am always willing to help out at ultra events if needed.