Eh, why not?
The main theme of the series would be about finding a balance between materialism and spiritualism.
It takes place about 100 or 200 years after Legend of Korra. Technology has continued to improve, and now the world is facing the Industrial Revolution (or at the very least, WWII levels of technological growth.) Larger kingdoms, like the Earth specifically, are growing more powerful while becoming more condensed into isolated cities. Bending as a whole has been on the decrease for several years, as people grow more and more reliant on new and fantastical technology; half of which can simulate bending much more easily. Linked with the decline of bending is also the decline of spirits, and the spirit world.
The main plot would be the Avatar attempting to prevent a growing war, as cultural ideas between all the tribes drift further and further.
The Avatar of this time cannot bend any element, and shows no drive to learn any. Partially because they were kept hidden from the White Lotus and never received any real training, and partially because they're just incredibly lazy naturally.
In fact, only their close friends know they are the Avatar. A large part of their arc would be finding their own 'spirituality' as they're forced to learn the elements to survive after being thrown into the center of the 'war,' and acting as the balance the world needs as a result.
The villains would be a previous, tyrannical Avatar who controls the current Avatar whenever he enters the Avatar state and wishes for a return to 'before the machines,' and a man pretending to be the Avatar by using technology to simulate bending while preaching a message of 'abandon your spirit worship and embrace the future.'But it's all garbage fanfic, in the end.