There are already light value (LV) and exposure value (EV) numerical systems. Why not use those?
Relating to Sunny 16 at ISO 100 (where EV = LV) we get 15 for bright sun, decreasing by one for each step in the sequence.
The system used by David Lyga is in fact strictly using the EV indication that we find on light meters. For ISO 400, 1/125@f/16 the light meter indicates EV17. The same exposure values at ISO 100 would be rendered as EV15.