This is a hard question, they might release a extra hard drive. Personally I would more like to see a dedicated VC channel and the possibility to play games from the SD card. Those cards is dropping in price quit fast and should possible be more cheap than a hard drive.
Of course I personally feels that it is not too unlikly with a HD, I mean are they using the USB ports for anything yet?
Buy it and pray to the gods of Sigs: Naznatips!