Mass starts are very difficult to combine with long hard tracks since you need a lot of cameras to follow the race. In individual starts there will always be some skiers passing by the cameras somewhere, if you lack coverage in a mass start you end up watching the woods and not the skiers.
Changing the 50K/30K in Holmenkollen to mass start was the ultimate shortsighted betrayal of cross country history. Winning these races used to have about the same prestige as winning a gold in the world championships, why would we need yet another mass start in a long season of mass starts.
It's like changing Paris–Roubaix to something completely different because it doesn't appeal to the tv audience in China.
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I would agree at least on paper. Even so the trouble is that even the largish hill in Oberstdorf is just 4-5min long. Quite often the obstacle itself just is not hard enough to create either gaps or considerable fatigue when done at a normal, consetvative race pace. Downhills simply allow too much recovery. To facilitate longer attacks one would need either something longer which is very tricky terrain wise, a long plateau on the top to force a longer effort (my favorite), or a quick succession of such 4min efforts to let fatigue build.
Burgstall climb is long enough. Take a Look at the gaps In the Skiathlon. Take a Look at Lillehammer. You do not necessarily need long loops. You have to have long climbs and a limited amount of flat sections.