While good in theory I suspect the average servo would wear out in short order under such service. Also the speed would not be very useful for standard propeller sizes that are designed to utilize thousands of rpms. Plastic gears and brushed DC motor do not make for reliable continuous service applications.
You probably missed the "disassemble" in my post. You disassemble the servo and remove the motor and electronics (no gears) for use. With the just the motor and electronics, you have a small high speed direct drive motor with direction and speed control, in effect a continous rotation servo without the case and gears.