The HD DVD drive doesn't need to be 2x. All that's needed is it supports 8x DVD speed. The only reason for wanting 2x HD DVD is for games which ship on HD DVDs. That's not gonna happen. Games will remain on DVDs, so an embedded HD DVD drive with suitable DVD transfer would work okay in the limited edition XB360. Of course, that would fly in the face of MS's claims to be 'neutral' and offer end consumers 'choice'...
When have they ever claimed to be neutral? They've said they won't force an expensive HD media format on consumers but a special high end edition wouldn't change that, the Core and Premium models still exist.