Strictly, I can't think that either Ethernet or USB can pass over the other. They are distinct hardware standards. What you mean is effectively packet-switched network protocols (things like TCP/IP, UDP, NTP, etc.) over USB cabling, vs. USB signals over Ethernet cabling.
Your "Ethernet over USB" is just networking over USB, which is common enough.
But USB signals over Ethernet standard hardware? I suspect that would be hard, or the USB standard would have just used RJ45 connectors from day one. Something might be possible, but I doubt you'd achieve the 5V supply's full rated current for example.
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