Modern chess is the culmination of centuries of experience, as well as an evolutionary sequence of rule adjustments from its inception in the 6th century to the modern rules we know today. While classical chess still captivates the minds of millions of players worldwide, the game is anything but static. Many variants have been proposed and played over the years by enthusiasts and theorists. They continue the evolutionary cycle by altering the board, piece placement, or the rules—offering players “something subtle, sparkling, or amusing which cannot be done in ordinary chess.”
Using AlphaZero to evaluate modified rules, to see which would be the most productive is a really interesting application of the AI. You can evaluate beforehand whether a certain rule change would make the game less or more balanced.