Currently the thinnest drives are 7mm thick, which is a bit too much for tablet makers. However DSI claims to have developed a new axial field motor measuring just 4mm and it should be able to power 5400rpm and 7200rpm drives.
Of course, the drives should be cheaper that solid state storage used in tablets today, but they will also be slower and more power hungry. In addition to tablets, the new drives could also make their way into ultrabooks. Combining them with small, yet speedy SSDs could be a very interesting solution for ultrabook makers.