I started thinking the only way it could even conceivably work was to send the completely
compressed MPEG4 data stream across the USB and then have the Hopper + do the heavy lifting. Sort of the way you can still watch HD and UHD from an EHD on a USB 2 port.
I'm pretty sure you are right on the money. Why? Well, here is my theory. Only the HWS and H3 are supported. What do these two receivers have in common, that also makes the H2K incompatible (which AFAIF has the same SoC as the HWS)?
The "Sling" capability, aka a video encoder of some sort. This encoder is more efficient then the MPEG4 that comes down from the satellites (H.264/5?), and allows for reasonable internet bandwidth usage with dishanywhere. So, Instead of the raw MPEG4 stream from the satellites, you are essentially going to see a Sling stream from the Hopper to the Plus device. This would also explain the difficulties that Dish is apparently having getting Multiview working.
But on multiple streams, if the Hopper + doesn't have an Ethernet connection where they could also create a MOCA path as well, I can't see how it could handle not just the local TV and also up to 4 Joey's at the same time.
I'm pretty sure the Joeys will pull the satellite video feeds directly from the Hopper, in the worst case scenario you are allowed up to 5 Joeys per H3, so that is up to 6 1080i streams, out of which 5 would be bi-directional to boot. It would be really inefficient to do it over even USB3. Same with DVR recordings, all still done on the Hopper itself, but the Plus becomes the coordinator.
The AirTV devices they make sort of do this already, they have integrated or external storage, OTA tuners and some logic to manage them. Then everything is streamed over LAN to your devices.