I apologize if its been covered previously, but has it been investigated to use ESC with a larger turbo?
Similar to this:
Like an series hybrid (EREV) drivetrain, the electric bits can make an impact where they are the most effective (high torque, low RPM). Once boost and flow rate are built, the electric motor disengages, allowing the battery bank to recharge... heck maybe you can even generate electricity when the turbo would normally open a wastegate.
It's still just wishful thinking, but high-speed brushless DC motor tech is becoming more approachable.