Okay so it's gonna be a while, but the Advanced Storage Technology Consortium (ASTC), consisting out of parties like  HGT, Seagate and WD, states that storage density expand 10 times by the year 2025. That would bopils down to 100TB HDDs (in 2025).

Perpendicular magnetic recording enables areal densities of under 1Tb/in² but new recording methods are expected to increase storage density to 10Tb/in² by 2025, paving the way for HDDs with a capacity of 100TB. Here's tachreport on this report:

Right now, we're in perpendicular territory, with areal densities under 1Tb/in². Shingled magnetic recording has already appeared in datacenter drives optimized for cold storage. Along with two-dimensional recording, a similar and potentially complementary approach, shingled tech looks poised to drive density scaling until at least 2017. That's when heat-assisted hotness is slated to take over, the crystal ball says. If the ASTC's projections are accurate, heat-assisted and bit-patterned recording will combine around 2021, pushing areal densities up to 10Tb/in² by 2025. In a four-platter consumer unit like Seagate's Desktop HDD.15 4TB, which packs only 625Gb/in², that density would theoretically fuel 64TB of storage. Well over 100TB would be possible with a seven-platter monster like HGST's enterprise-oriented Ultrastar He8.

Now, the ASTC's members won't necessarily hit all of their targets—a lot can happen over the course of a decade. But this is the plan as it stands right now. Kudos to Forbes contributor Tom Coughlin for being the first to publish the roadmap.

HDD roadmap predicts 100TB HDDs by 2025