The Arduino protocol is fantastic, it really sets PCLC apart from the competition.
But I would love to see >1 Arduino supported at some point in the future.
Arduino clones are very low cost ($2), so it is easy to imagine your starting lights containing an Arduino, the Race Director console (for giving Stop/Go penalties) would contain an Arduino, the fuel level display contains an Arduino. Each of these could be in a different place on the circuit. It is better to run one USB cable to each of these modules, instead of hundreds of signal wires connected to one central Arduino Mega.