I think you mean you would prefer that VOXL supports PCA9865 natively.
We have an I/O library ready to go, libvoxl_io. voxl-i2c is an application that is an example of using libvoxl_io for i2c commands.
One would need to implement the PCA9865 i2c protocol using libvoxl_io to control that part externally from VOXL.
As mentioned previously, Flight Core has native PWM support if you were to send over MAVLink