Where the fuck are huge parachutes for whole cabin? Totally technically plausible.
The flight recorder revealed the passengers were calm until seconds before the crash, there was no time to evacuate even if they had parachutes.
It's harder than you might think. Usually people are afraid of heights and would hesitate or even panic before the jump, so the evacuation would take at least 10 min. What is more, you wouldn't be able to use front doors because they would be sucked by the engines, so everyone would have to jump out the rear.
No, there is no way to provide ejection equipment for passengers. They could be provided with airbags,which would help in some cases.
The air at 38,000 feet is so thin you cannot survive without immediate and continual pure oxygen such as from an oxygen mask. It is really, really cold. Like -50C. This is why in a depressurization the pilot must dive the aircraft to immediately get to a safe altitude like 10,000 feet.