Today's capacities of HDD are enough for many task, so I have an idea how to increase performance. As I think, this idea requires not much changes in manufacturing process(in simple case it requires firmware update)
So, an idea is to make per-platters RAID 0 rather per-disk. Modern HDD contains minimum 2 platters, so each of them may functioning like single disk in RAID 0 or 1, or it possible to use 4 platters for higher RAIDs.
Externally such drive remain visible and functioning like regular drive, but internally it has a RAID controller in 3,5" or 2,5" package. With RAID 0 realization(for example: 2 platters for 500GB each) it allow to increase reading/writing performance and utilize modern interfaces like USB3 or SATA3.