> Since (M.2) NVMe to USB adapters exist, protocol conversion is certainly possible, and since such adapters are surprisingly inexpensive, presumably there's enough demand to drive down the price of the underlying controller chipsets.

> (These chipsets are, for example, the Realtek RTL9210B-CG or the ASMedia ASM3242.)

The NVMe to USB adapters aren't converting the NVMe protocol to another disk access protocol. They are USB3-connected PCIe endpoints, which allow the PCIe NVMe drive to connect to the host as an NVMe device.

This isn't equivalent to the protocol conversion the author is seeking, which would accept SATA commands on one end and translate them to NVMe on the other end. I would actually call that SATA drive emulation, not protocol conversion, as SATA and NVMe aren't 1:1 such that you can convert SATA commands into NVMe commands and vice versa.