Has Nintendo stated that you can install games onto an external HDD? If this is USB 2.0, isn't that going to have serious loading problems? It wasn't an issue with SD cards on the Wii or DS since the games are small. But if you download a 5 GB game for the Wii, aren't the loading times going to be very poor going through a USB cable? I'm not even sure if they are only going to allow media via USB.
Real-world USB2 speeds are about 30MB/s, the Wii U's optical drive reads at 22.5MB/s, so you might even get slightly faster loading speeds from a USB hard-drive, although the difference between the two probably won't be noticeable.