That's why mega capacitors are so interesting even if they can't store as much as a battery. We could instantly store all current kinetic energy in it and then

That's why mega capacitors are so interesting even if they can't store as much as a battery. We could instantly store all current kinetic energy in it and then recharge the battery "slowly" with the energy from the capacitor. I agree about your second point, mechanical brakes are very simple and reliable. I'm pretty sure we will forever have them in our cars for safety/emergency reasons.