It is possible with the right kind of arduino chip
and the right firmware for it to make something that looks
like a USB drive. (At least I think I figured out that
was possible once).
I keep hoping someone will combine that with a network
interface so I can make a NFS or CIFS filesystem
appear to be a thumb drive to a stoopid TV that refuses
to read file shares, but can play anything from a
thumb drive.
So far, I haven't seen such a gadget. (I wonder what
the response would be on kickstarter, but I'm not
gonna implement it :-).