A better title for this thread probably would have been
"The future of the light helicopter is not turboshaft".
I doubt we'll see battery technology advance enough in the next 20 years to make a pure electric helo drivetrain a commercial reality. But that doesn't mean we won't see some progress with various hybrid drivetrains.
For example, how about a set of
variable frequency free-piston engines with linear generators, that cycle on/off based on demand. These engines are very lightweight and can operate at high cycle pressures, giving extremely high thermal efficiency. Their overall BSFC rate would easily be half that of a small turboshaft engine. And if you don't like electric drivetrains, how about free-piston engines and a hydraulic drivetrain? Or if you want to be carbon-free, how about a free-piston engine that operates on ammonia fuel?
To determine what approach might be best, one needs to objectively evaluate the entire rotorcraft drivetrain's particular requirements, including cost , weight, efficiency, reliability, etc. Simply taking the position that
"electric is green, therefore it's the obvious choice for future rotorcraft drivetrains" is a bit closed-minded.