It would be nice if one could eliminate the reliance on NFS altogether. That is, it would be ideal if Linux could mount an HTTP-based (read-only) filesystem from which it could grab all of the necessary files. This should make it easier for projects like J-Receiver to work on systems that do not easily support NFS (e.g., Windows), or in scenarios where the user cannot or does not want to export a mountable filesystem via their NFS server. Does an HTTP based filesystem already exist for Linux?

This was something that we did for our SPIN extensible operating system at the University of Washington a while back, and it was generally considered to be very useful.

However, this may require that one replace the currently flashed (or ROMed) Linux kernel with a new one on the Rio Receiver, as I believe it boots things via NFS. I don’t know if this is possible.

How about WebDAV? This is an open protocol that runs over http and provides basic file semantics. May be overkill though.

Unless you reflash the kernel, which is not easy, this isn't possible. Besides, Windows can support NFS, obviously. We do.