How do you envisage it working in practice? If a plane had a disaster that will make it crash in a matter of minutes, people wouldn't form an orderly line to jump out with their parachutes. And if the malfunction is not making the plane crash in the next 5 minutes, the plane can probably land safely at the nearest airport.
Not necessarily. I've flown on many flights where the first class has its own door at the front of the plane, and the lower classes have their entrances further down the fuselage, so that the first class isn't bother by the boarding plebs. I fly pleb class btw.