Yes, looks like all the solutions I've seen involve Wi-Fi tunneling the USB protocol. Just got a reply on the Helicon Remote forum saying that the Wi-Fi version, when it becomes available, can even be implemented by hard-wiring one smartphone to the camera and then using a second smartphone remotely (i.e., wireless) to do the controlling. I can live with that!
I think the likely problem with trying to extend beyond, say, 10 meters (wired or wireless) is going to be a matter of latency. It's not going to be that big a deal with controlling autofocus and shutter release or even remotely changing camera settings. It probably wouldn't present that great a problem downloading a captured image, really just a file transfer. However (and this is of interest to me for some of the uses I've got in mind), Live View and video might present a real problem. I suppose we'll find out when we find out.