How big would a HD drive need to be? I don't quiet now what the size of the Wii's internal memory is (besides I have 1500 blocks or something like that left, no idea what it means though), but would an external HDD need to be more than, say, 10GB? A 10GB HDD would be dirt cheap I'd imagine, since last time I checked I can get a 350GB or so external HDD for $125. I'd also think 10GB would be more than enough, even for people downloading mega amounts of VC and WiiWare games, and whatever DLC ever comes.
I would like to see them add support for both playing games off of SD cards and support for a HDD, that way depending on what you want you can have it. I'm not sure if I'll ever need it, but at least there would be two options if the need ever came up.