I wonder how much effect something like "the Wim Hoff Method" would have on survivability. I can personally vouch for said method allowing me to stay cross-legged meditating on my balcony for an hour in -15ºC weather, while still remaining warm to the touch. Obviously, the altitude and atmosphere would play a significant role, but I've seen videos of that guy taking elderly people up Kilimanjaro in their underwear, and they turned out fine.