Here's my pet theory on the death of hard drives: it'll decline fast when SSDs hit twice the price per TiB, and we're only a few years away.
My thinking is that there's a lot of corporate deployments of four drive RAID 10. With SSDs, you can make that two drive RAID 1 with equivalent redundancy, but much, much faster.
Spinning platters are around $10 per TiB. SSDs around $60. (This does depend on the specific models of each.) SSDs would need to be cut in half about 1.5 times to reach that point.