I'm not suggesting that FPGAs are easy to exploit; I'm saying that the premise that they are fundamentally secure and/or the only way to implement this requirem

I'm not suggesting that FPGAs are easy to exploit; I'm saying that the premise that they are fundamentally secure and/or the only way to implement this requirement is wrong. Having a hypothetical discussion about how an FPGA might be attacked is not the point. Your entire premise is a handwaving argument reliant on security by obscurity, and furthermore its not even correct. Once you can reconstruct the netlist its game over.