"But what games announced will use it?"
More than likely, if it's actually released, it will serve only as a "Big Ass Memory Card". I can't see Nintendo pulling an "Expansion Pak" at this point in the game. Plus, if they made a game that used the hard drive, they would have to make the game also accessable for people who don't own it, unless, of course, they included it in a big game (like the EP for Donkey Kong 64 or Majora's Mask)
But I think this is just a rumor though. Probably rumblings of what's to come on Nintendo's next system.