Rockbox does not currently have a USB Host implementation, or any kind of network stack to actually use a network device for anything. This would take a gargantuan amount of work and nobody has even indicated they are interested in starting it.
This kind of thing is much more likely to happen on the Rockbox-as-an-App targets like Android, where the OS provides the ability to get a stream from the network and we would only have to deal with actually playing it (the part our code knows how to do well).