Multiple boards autodetection circuitry
My first comment is that you are over thinking this for only 100 boards. Also drop the idea of a matrix and just put north and south connectors and chain them together in a linear vector. That greatly simplifies the auto address selection. Each board in turn is only visible until the one before it has been setup and identified.

The overall scheme to test in this way carries too much cost burden on each board's BOM. Even the chip SLG46826 probably adds too much burden.

I suggest that a far better method is to remove all the extra connectors and special address selection circuitry and instead add test point pads on one side of the board. Then build a simple text fixture with the needed number of pogo pins that can engage the test point pads on the board under test. Each pogo pin is connected by wires over to the "mother board". Any special circuitry to aid the mother board's ability to manipulate and monitor the board under test is placed upon the mother board. In fact if each board is relatively small the pogo pins and necessary alignment posts can be sited directly on the mother board thus saving the discrete wiring from the pogo pins. 

Using this scheme it is quick to engage each board for testing it and the board under test needs no manual configuration. In the case that 100 turns into 1000 boards you can simply duplicate the motherboard and pogo pin fixturing to setup additional test stations.