It is easy to implement, but this app is designed for 3D printer firmware like Marlin or Repetier etc. and I think they all use 8bit pwm by default.
But I will think about that, because it will be helpful for some peoples, who have powerfull lasers and >8 bit pwm resolution.
So, if I understood it right, you have GRBL firmware on your machine? If so, then you definately have to try LaserGRBL software. It is much powerfull and was designed especially for GRBL firmware. ImageToGcode is not supporting GRBL.