Welp, Now most of the pillars are dying from the marks. What a development. I can only hope that they'll figure out how to stop the progression... Maybe the humanizing drug? Since the marks were said to resemble demon marks. Even Tokitou, who's the youngest, is now the closest to deaths from injuries.
And if what Kokushibou said is correct, it's looking very grim for Himejima.... He might even die from the mark in the middle of fighting Muzan, if not sooner. It's hard to see him having the chance to even take said drug, which is already a Longshot.
If the person with mark who survive is that swordsman in the ancestor flashback, it make sense that Tanjiro will be the only person to survive the mark.
And speaking of Pillars, Tengen doesn't have the mark. But I can think of a development.where New UM5 attack them > turns out to be Tengen's brother
> Tengen manifested mark to both protect Ubuyashiki descendents and defeat evil brother. Although I can also see that encounter might prove fatal for both retiree guard squads...