But all of those cases should be governed by a very simple overarching rule: If the laptop lid is closed, assume that it is in a closed bag with no cooling available to it.

Because that is the usecase that hibernate is for. It makes laptops convenient by allowing you to just close the lid, put it in a bag, go somewhere, take it out of the bag, and then open it and continue working. If you need to tell people that they need to shut down their computers properly before putting them into bags, you have just produced a vastly inferior product.

This is an area where Microsoft desperately needs a Chief-making-it-not-suck-Officer. Someone who can just take that surface laptop, notice that some idiot actually wrote that you are supposed to shut it down instead of hibernating to put it in a bag, and yell at people until the product is fixed. Because right now it's broken.