Well I've been pretty involved in storage for the last 10 years, 5 of them at Network Appliance and then later another 4 at Google dealing with their storage scale. And worked with both Seagate, Fujitsu, and to a lesser extent Hitachi as they have worked to increase the density of what can be reliably recalled. More interesting has been watching the struggle of thermal noise and the ability to push past areal densities of 300 - 400 Gbits/inch^2.
There are certainly nano-scale technologies which seek to store information in the 'spin' of electrons (I'd be hard pressed to see you get better than that) but may become impractical if the network bandwidth gets to the point where the size doesn't matter any more. Specifically, what matters to the end consumer is that they can get what they stored into something which can use that information. If it comes from disk across the room that is just as good as a local on board disk if the bandwidth is the same.
The effect this reality is having on storage is that fatter (and increasingly more fragile) drives, are becoming less useful to consumers than larger but more reliable storage attached via a protocol (be it iSCSI, iCloud, S3, or NFS).
So once people are unwilling to pay to carry it around, the ability to recoup your investment in making it possible to carry around a device that can read electron spin is less and less likely. And your s-curve will become clear, when for the last 5 years the drives have all been at most 6 maybe 10TB and the price of those doesn't seem to fall all that much.
I realize disk growth has been phenomenal "your whole life" as CPU performance growth was for most of mine, but CPU performance growth has kinda sputtered big time. We've been multi-coring for a relatively long time now. Storage systems (especially random access read/write systems) are in the same boat. But the glory days are over.
I am curious to see if storage will have its 'multi-core' moment. That will be interesting if it happens.