SSD bandwidth will ultimately be limited by the amount of PCIe lanes you have available (for something other than the Apple Silicon internal storage). So the approach has inherent limitations. You can of course scale out to multiple systems to get more throughput.

You can use this approach with Intel Optane, which is wearout-resistant unlike NAND and can thus substitute for RAM. Last I checked, it was available quite cheap on the secondary market, ~$1/GB as opposed to ~$15/GB or more for DRAM. (Of course that's nowhere near as cheap as NAND, which is around ~$0.1/GB but quite wearout-prone with heavy writes.)