Hey guess what, the black screen happened to me today, just as I predicted before entering the Shop Channel for the sake of prompting my long-disconnected Wii to reconnect to WFC services (before jumping onto Mario Kart). The electro-handshake was in limbo for a bit, so I powered down, restarted, went back to the Shop Channel, and it tried to black-screen me again but it didn't last long this time and the Shop loading screen came about fine.