Mind you, a lot of these issue are going to get complicated again - for a time, anyway - by the introduction of high-speed
non-volatile RAM such as
3D XPoint, MRRAM, Phase-Change RAM (which may or may not be what 3DXP actually is - there seems to be some distrust toward Intel on this, given the IP concerns it would have), CBRAM, or SONOS (depending on whichever proves most practical, with 3DXP getting an early lead as it is already out the door).
Setting aside specialized uses such as Optane, the long-term impact will probably be, on the one hand, an increasing shift to OS persistence and a move away from explicit disk access and file systems, and on the other, a multi-tier memory structure where each layer - DRAM, NVRAM, high-density Flash SSD, mechanical disk, and then finally long-term storage such as tape, optical, and possibly some of the newer ultra-high-density/stability storage systems such as millipede memory, SMR, and HAMR.
I expect that the two tendencies will reinforce each other, as multi-tier memory management will be demanding enough that a much if not all of the management of it will need to be handed over to the OS, even if conventional file systems remain the order of the day.