Disk ???
I think the hybrid disk employs the same old methods of cache memory. You a large and slow memory (the RAM) and a fast and small memory (L1 cache). The end result is that you have the statistical effect of a large and fast memory. So hybrid disks will be a good options.
But I am not sure if we need a disk anymore. Why not just plug the non-volatile flash memory directly on the computer bus (PCI)?