I rode La Marmotte in 40 degrees heat. Im an amateur, decent climber on my day, but Im everything but a pro. I live in Denmark where we can experience 25 degrees if were lucky, but usually summer is around 20 degrees. I was fine. It was hard, but I was fine. So were everyone else I knew who was racing that day. And La Marmotte is harder than any of the stages they are riding this year (stage 12 is very similar, only noticeable difference is Galibier N >>>> Galibier S).
Like please, these riders do nothing else than train, and often in very warm conditions. If they are shortening the stage or doing anything else, I'll be extremely disappointed and mad. 40 degrees is a lot, especially at the bottom of Alpe d Huez which by far is the hardest point of the race due to fatigue, percentages and heat exposure, but pleeeeeeeeease.