At first power-up, I had a USB-10/100 ethernet adapter connected to the USB port, and I was watching the log on the DHCP server. The TV did get an address with the shipping firmware. However, it would not connect to the Roku server, download, or configure channels, nor would it download the current firmware. I did have to put the TV on a wireless network for it to go that far. I used a temporary network on a small portable WiFi base station I keep in my laptop bag.
Once the update was installed and the TV rebooted, I shut down the WiFi base I had connected it to. The TV continued to work just fine (connecting to Netflix, Amazon, and CBS) over the wired ethernet connection.
This ethernet dongle is based on the Asix AX88772 chip. These are very common, and very cheap. If you were developing a small embedded Linux system (like the Roku) and needed USB ether support, this is definitely a driver you would include in your kernel. The AmazonBasics USB 2.0 adapter
uses this chip, as does this other one
, which I used. Both are under $10 each.