They forecast that the storage capacity should double by 2016, but also plateau as it would be the maximum performance offered by the current perpendicular recording technology. Beyond, it will probably involve new technologies that still need to be validated. In 2016, we could expect 8 TB 3.5" HD while 2.5" units should offer around 2 TB. BEyond that date, new technologies based on surface heating, might allow plate-based HD to further increase storage density, however, it remains unclear how this would impact power consumption of such storage units.
By linathael, original by Lionel