We need a training facility in the high tundra of Alaska obviously. But even with all that ...very very few folks are really capable of serious prolonged exposure above 3500 meters. Maybe some Tibetans or Peruvians or Bolivians or Nepalese. I think I read where there are Bolivians that live at 17,500 feet or so....that's damn high...I live at about 1000 feet or 800 feet above downtown Nashville. When I go to our mountain house in NC at 4800 feet, I can feel it a little. I remember as a kid in Quito at around 10,000 feet that ciggies would go out on their own in an ash tray...that tells you something. You almost have to be born into it. I spent a few weeks in the Sierra Nevada (NE Colombia)at nearly 5000 meters..(the peak at around 20K feet is the largest relative elevation rise in the world going to about 20K from sea level on the Caribbean in 30 miles. Anyhow, I got sick...and once you get sick...you're more prone to it in the future.
Just my 2 bits....it's a ruff ruff environ to fight and carry all that gear in. Adrenaline skin poppers and beta blockers will help....aspirin too.
Regards