One of the features that this project can provide (if implemented) is with helping each node find its static address.
Usually one would either use DHCP or static IPs for the Ethernet port. DHCP makes it tedious to know who is who and requires a master node to handle probing the network, while static IPs require a manual management, at least modifying each config file during the SD card duplication. Tedious.
The FPGA provides 4 ports and is intended to communicate with other quads, so each FPGA has its own address, that can be setup with jumpers/DIL switches/hex encoding wheels/whatever. And each Pi port is static so it can have its own fixed address.
Let's say there are 4 Pi ports, so 2 hardwired bits, and the FPGA can fetch its own address from a few GPIO pins (to a 74HC165 or 4017 for example, or even charlieplexing? SPI requires 4 wires, I²C only two but is more complex). This port address can then be read/fetched from the respective Pi which will then execute the program related to its address. Let's be reasonable and say we have 6 bits for the quad address, that makes a byte for each Pi which can then configure its own static IP address. That would be the best of both worlds :-)
Another aspect is that, if several quads need to be connected, each quad must know its own address to send and receive packets. No routing is possible without addresses.