A company called Micron is developing non volatile storage to fill the latency gap between pcie storage and sdram. Almost certainly requires new mobo architecture and might require more trivial kernel changes, but nvme tech is already pushing the limits of the north bridge.

In 20 years we'll probably see this in line production. In 40, we might see non volatile storage replace volatile memory for most use cases except things that need to be volatile, such as symmetric crypto keys.