This is what SSDs already do on current-gen consoles and PC. SSDs act as the cold storage, and it's read from the NAND on the cold storage and placed into the available system memory. From there, the data is operated upon by the CPU and GPU as needed.
The "next gen" that graph alludes to is the speed in which the data off NAND is being packaged and moved into system memory, but the technique itself, at least indicated by that same graph, is nothing new. Not necessarily, anyway. And there's ways that interconnect protocols over PCIe 4.0 handle signaling and packaging of data off NAND modules that's fundamentally different to the way volatile memory controllers do the same off main system memory (not to mention the levels of granularity in data reads, writes, and modifies that govern NAND vs. volatile memories).
If either of these systems were using a form of persistent memory, like Optane DC memory, interfaced with a DRAM memory controller, then that would be a lot more in spirit to the "in some ways more like RAM" line in the graph. As is, I mean, yeah, it kinda is in some regards, but in many others it's just fundamentally different and nowhere near that level.