USB to Ethernet? No, thanks.
Ethernet, as implemented in current MacBook Pros, has a theoretical maximum speed of 1000 Mbps (1 Gbps; 125 MBps). The current USB to Ethernet adapter is presumably only USB 2.0, which has a theoretical maximum speed of 480 Mbps (60 MBps). Currently (over 1 Gbps Ethernet and with a 7200 RPM drive), I can download files from my local server at speeds that peak over 720 Mbps (90 MBps). This speed exceeds that of USB 2.0, and would thus be bottle-necked by such an adapter.
New WiFi standards may have a theoretical maximum of over 1 Gbps, but that probably assumes new infrastructure, no interference, and numerous other laughably impossible conditions. Another thing WiFi lacks over Ethernet is signal consistency.
If a USB 3.0 to Ethernet adapter becomes available (which is likely), it won't be so bad. However, it means I have to carry yet another adapter with me. Having to carry extra stuff to shave a few ounces of aluminum does not help me. To "hook up" in a standard work place, I might need to carry a Mini DisplayPort to VGA adapter, a USB to Ethernet adapter, a MagSafe adapter, and a Thunderbolt to FireWire adapter.
The "pro" market typically wants more [practical] options, not fewer.