It's another level in the hierarchy. DRAM is too slow to use as SRAM, but it's denser, so it has a place. Flash is too slow to use as DRAM (or PCM), but it's denser, so it has a place. Spinning rust. Tapes. Adding another layer between DRAM and Flash to take advantage of its unique trade-offs is not only reasonable, it's exactly what we always do.