DigiTimes suggests that these changes to the circuit layout were made with the sole intent of preventing piracy by blocking these warranty-voiding installations. If that's the case however, why did Nintendo only take steps to block just the WiiKey, a modchip that was released only several weeks ago?
There were similar concerns in the past about Mario Kart DS updating the Nintendo DS' firmware as an anti-piracy measure, but it was quickly discovered that the handheld was only saving its WiFi settings. It seems far more likely that Nintendo has had the Wii's revised motherboard planned for months, and that locking out any modification methods was an unintended result.
Nintendo Wii console