"OCZ Vertex 4 SSD (512GB)"...only in your mind and nowhere else. "This is all pure speculation though with no rumours either way to support the presence of an SSD. An alternative to a removable/replaceable drive, would be memory chips soldered to the board, this would provide a basic amount of storage for every owner and be a lot cheaper than adding the interface and bay space for a removable drive."
Why on Earth would a gamebox maker use a very expensive, unecessary, 512GB drive when they can make it much, much cheaper using a hard disk? Some (maybe all) Xbox 360s used Samsung disks; Samsung disks were bought by Seagate. Segate also make hybrid hard disks.