@xan @xssfox I've actually been wanting to do a slightly-more-modern version of that for retro game consoles that are just a little too retro to support proper netloading, allowing me to fit my whole collection on my NAS instead of "a random USB disk that may or may not be compatible with a particularly picky USB stack" (see: the wii is very picky about what flash drives it works with, or at least it was when I tried that...)
It's actually fairly easy to do this with USB and a pi zeroW or similar, since linux's gadget framework supports mass-storage emulation, and there's nothing stopping you from setting the backing 'file' to an iSCSI LUN (or even going full passthrough mode for some reason)