> It would certainly send a strong message, and cause a lot of chaos, if the biggest CA on the Internet found itself being removed from trust stores. Yet, there's no particular reason it couldn't happen. How exciting.

Trust stores and Browsers specifically have more options than simply remove a CA. A more reasonable approach for distrust process of a CA this size would be to stop accepting any new certificates issued after a certain date. Then existing customers will have a heads up and even if asleep will find out the bad news during scheduled renewal rather than while the responsible employees are on vacation.