Last year Amazon entered the TV-box game with the 1st gen Fire TV, and this year the device got a nice upgrade with the 2nd-gen Fire TV. Just like last year offering, the new TV box runs Android and almost everything running the green robot system can be rooted, although there isn't much point by doing so because it doesn't make that of a difference. Still, if you want to put your hacking genes to work, XDA-Developers member, zeroepoch, found a tricky way to root the new Fire TV, although you will need to make a hardware intervention.
Differently from the 2014 Fire TV where you would just patch a software, the new one needs a piece of hardware to be soldered before the patch. This has to be done carefully, as you need to open the box and solder a connection for a TTY UART device. Although obvious, it is important to remember that you will be playing directly to the hardware and any wrong move can damage the TV box. After the hardware is installed, you can connect the device to a computer in order to make the rooting itself. For this, you will need a computer running Linux with Python 3 and pyserial installed and a USB A-to-A cable. You will also need read/write access to /dev/ttyACM0 which quickly shows up early in the boot process, and preferably ADB to help with the handshake process. You can read the complete guide on the source link below directly on the Xda-developers thread.
Last year's model had a downside - if you rooted the device, whenever Amazon sent a new update, the root would be broken. This new method changes the system partition and when it is done, the Fire TV will be unable to install automatic updates. The downside is that any software update will have to be done manually. It is important to note that you shouldn't proceed unless you know very well what you are doing, you are familiar with Linux and you are willing to risk bricking your Fire TV if anything goes wrong. Nonetheless, it is always fun to play with Android and Linux, so, enjoy the process, although it is a bit long with an average duration of 2 hours.