Chan,
That is already done courtesy of the properties of the Cadmium Sulphide.
The surface resistivity reduces in an exponential way with an increase in the photon density. The photons raise electrons to the conduction bands and increase conductivity, and resistivity is the inverse of conductivity.
The conventional exposure steps of shutter and aperture are also exponential.
So we don't have to worry about that in the circuit which is why they originally were able to just use a passive linear circuit to drive the meter which is also linear.
There is a circular slide rule on the lens barrel that allows conversion of the meter reading to shutter and aperture setting