Hmm, I was thinking something like the accelerator light real F1 cars have. Brake light you say? Hmm even more interesting.
From a manufacturer's point of view is quite easy to have an extra LEd output that would double the LEDs on the ESC itself. That way, brake, acceleration or both (functions) you get a nice flashing light going.
I am not that keen to open an ESC to hardwire the extra LED myself especially since it is quite likely some company already did it for me.