Flywheels can be amazing, but they can also be expensive and dangerous. He gets a low efficiency return, poor performance, much added weight and risk of losing body parts to the spinning wheel under his XY chromosome parts. Sadly, the on,y way to make the transmission effective is to run it electrically or with a very complex and too large for the space CV transmission or with controlled vane torque converters. Since electric is so easy and available, you then to realize that replacing the flywheel with some supercapacitors or lithium’s would be much higher energy storage and cheaper and smaller and more effective. Don’t get me wrong, I love mechanical over electric, but for this instance I think I’d go electric.... at least at this time in history.