Those are great ideas! I'd be up for working on those. So you're actually thinking to replace the flywheel of an engine instead of refitting the brakes? (I'll put my heatpump comment in a separate comment)
Actually what about putting in a bigger alternator and stronger belts and having it charge some super capacitors? That's already connected to the engine through a belt so whenever you use engine braking you could also be partially charging.
Can the alternator run in reverse though and provide energy to the engine/drive train?
Well it was just an idea conceived over 2-3 beers with a friend with just some basic napkin math that said we don't brake too much of the laws of physics. I can see multiple approaches working.
But the goal - make the existing fleet of vehicles better while cleaning the air as a bonus is a worthy one and smog is a first world problem.
"Hybrid automobiles replace the separate alternator and starter motor with one or more combined motor/generator(s) (M/Gs) that start the internal combustion engine, provide some or all of the mechanical power to the wheels, and charge a large storage battery. When more than one M/G is present, as in the Hybrid Synergy Drive used in the Toyota Prius and others, one may operate as a generator and feed the other as a motor, providing an electromechanical path for some of the engine power to flow to the wheels. These motor/generators have considerably more powerful electronic devices for their control than the automotive alternator described above."
Can the alternator run in reverse though and provide energy to the engine/drive train?