Another problem with aiming for very high altitudes is that you need to have several hour long flights to be able to reach those altitudes and really gain anyth

Another problem with aiming for very high altitudes is that you need to have several hour long flights to be able to reach those altitudes and really gain anything. A typical climb/descent rate for a passenger jet is 1500 to 2000 feet per minute. So for a normal flight, going up and down to 35k will take close to 40 minutes. Going to 55k will take an hour. So this means you can't start small and focus on cityhoppers with the fancy high-flying electric planes, you have to go straight for competing with the heavy jets.