There's no way you could (or should!) connect the HD-DVD in place of the HD, and again re-connect the HD on the HD-DVD, that would make the whole unit hideously long!
It's difficult to imagine the HD-DVD to be stackable on top or bottom of an horizontal xbox360 either, because of the "sucky" )( design (unless they are going to make the HD-DVD unit "bulby" () , "smiley" )) or "frowny" (( depending if it's supposed to be top or bottom or versatile.
Had MS planned this more than minutes before the CES keynote, I'm sure they would have designed the xbox360 with an external/replacable HD-DVD in mind.
It's difficult to imagine the HD-DVD to be stackable on top or bottom of an horizontal xbox360 either, because of the "sucky" )( design (unless they are going to make the HD-DVD unit "bulby" () , "smiley" )) or "frowny" (( depending if it's supposed to be top or bottom or versatile.
Had MS planned this more than minutes before the CES keynote, I'm sure they would have designed the xbox360 with an external/replacable HD-DVD in mind.