not if you jumped out the back doors

The logistics of getting upto 568 people "crash course" trained in parachutes at the start of each flight is a big task.

Not to mention the logistics of getting 568 people shitting themselves into parachutes correctly, lined up in an orderly fashion at rear doors in a depressurised plane cabin and actually jumping out Imagine just how long this would take!!!!!!

Not to forget the fact that the vast majority of crashes occur during the landing and takeoff phase of flight. It is rare for planes to crash suddenly in the cruise portion of flight.

The ejector seat idea might be possible to install on a ripple firing basis similar to some military bombers, and the altitude oxygen issues is simple, dont eject till low enough to survive. The big problem with the ejection idea is again the training side of things, not to mention that ejection seats are very very heavy pieces of kit and to fit say a 747 that on average holds 400 people with such seats would mean it would never be able to take off, let alone designing in the necessary structural weakpoints and explosive charges to blast off the roof, yet adding additional strengthening to ensure you dont get fatigue failures around the jetison roof!!!!