According to our friends GoNintendo, the latest episode of the IGN podcast hints rather strongly that Nintendo may be making some announcement regarding a hard drive attachment for Wii at this year's E3 games exposition. Apparently the reasoning behind it is the large file size of Neo Geo Virtual Console games. IGN are supposedly the 'people in the know', so this one might have some credibility, but personally - I'm not holding my breath quite yet."
It's actually a fair point about the Neo Geo ROMs, they were bigger than N64 games, but they weren't huge by modern storage standards. Nintendo have included a couple of USB ports on the Wii, it even powers up a USB Hard Drive, so in theory its totally possible. Nintendo's only major concern with allowing USB hard drive is the risk of pirates booting disc images direct from the drives.
Either way, I'm sure we'll have some good news across the board when the new E3 rolls around next month.