Now granted, I know nothing about building or certifying helicopters, but surely in this day and age the obvious solution is a couple of Tesla-style motors driving the rotor? Redundancy in lieu of certification. Powered by a cheap and efficient motor/generator through a small battery to provide 5 minutes of extra T/O power and to negate the need to autorotate.. or have the option to strap on an extra motor/generator and turn it into a twin..