It was quite surprising to discover that the Amazon Fire TV Stick 2 works with USB OTG cables out of the box without needing to be rooted. Some, including myself, questioned whether the functionality was accidentally left enabled, and if a future update would disable OTG cable support. The good news is the 184.108.40.206 software update not only still works with USB OTG cables, but it actually better supports USB ethernet adapters connected through OTG cables.
The older 220.127.116.11 software version allows you to connect the Fire TV Stick 2 to your network via ethernet by using a low power USB ethernet adapter coupled with an OTG cable. The only issue was that you could not manually configure the wired network because the network options came up blank when accessed.
With the new 18.104.22.168 software update, and its new interface, you now have the option to manually configure the wired network settings when using a USB Ethernet adapter with the Fire TV Stick 2. The options available are identical to those found on the Fire TV 2, so you can manually enter an IP address, a gateway IP, subnet mask, and DNS values.
I did verify that external USB storage does still also work with this new software version via an OTG cable. You still can’t move apps to external USB storage on the Fire TV Stick 2 because the device still limits this to microSD cards, even though there is no microSD card slot. The Fire TV Stick 2 treats external card readers as USB storage, so that won’t work for app storage either.
Big thanks to Roberto for first discovering the manually configurable USB ethernet adapter and pointing it out in the comments of an earlier post!