My understanding from talking to the Surface Engineers the spine doesn't offer enough data bandwidth for anything but the keyboard and mouse. I guess a 3rd party could create a blade that had the radio and antenna and nothing else...
MS is releasing a Surface 2 with LTE very shortly....
You mean, the cover is nominally a USB device, but it isn't really USB? That is, a "USB" device is supposed to follow certain protocols, so if significantly deviating from those protocols, it isn't "USB", strictly speaking. If I'm following what you're saying, the Cover interface therefore isn't "USB" and my calling it USB was a bit misleading.
Of course, I made the mistake of assuming it was USB because of the device description, classification, etc. in the documentation. I know it's an arcane point, but also shows how easily misunderstandings can arise, and while not applying to this discussion, under unfavorable conditions, could spark wild speculation spiraling out of control.
No doubt at all that the engineers had valid reasons for design decisions made, but could it be, were MS to provide a bit more information about the Cover interface, it would save you the trouble of having to explain it yet again...?