... If I added a 1of4 analog switch and used the 2 available lines then I could sequentially sense each of the 4 thermistors, allowing separate readings for each quad. I could then relay them as status values for the driver to decide what to do. IS this something that is worth added cost of a switch chip?
I would say 1 sensor for 16 chips in the center on the heatsink. The heatsink will spread the warmth more or less and a sensor in the middle will probably pick up close to the highest temp of all 16 chips.
This is better way than measure in different spot and calculate average.