One of the things people requested of the Empeg "back in the day" was for it to emulate a USB mass storage device for the purposes of managing the music collection. That would have been too costly in terms of development time, its database architecture doesn't really support that. Plus, the USB cable was much slower than the ethernet cable anyway.
I can see how a read-only implementation of this could be fun and useful, though. For instance, there are a lot of consumer devices with usb slots that claim to be able to play media from a USB mass storage device (such as a memory stick). Sure, putting your music collection on a portable hard drive makes more sense, but imagine that you still have your empeg sled installed in your car, and you've driven to a friend's house, and his TV has a USB plug on it, and you want to play him a new album. Scrounge a 12v power supply and a USB cable and you're there.