One thing I noticed is that there's a clear distinction between the "world" of Honnoji and the "world" of Revocs on the show. This distinction has also been alluded to in several of the show's motifs.
Satsuki's world is a child's world. She is extremely powerful and capable, but plays in a sandbox. As she grows up, her sandbox gets bigger, and she has more ambitious ideas, but everything is still a game. Her conquest of other schools and her domination of Japan is just a juvenile re-enactment of the Sengoku era, without the fatalities. I don't think she has ever killed anyone, nor has she ordered anyone killed, ever. When battles are lost in this world, people get embarrassed, not killed. When you fail utterly in this world, you get expelled, and that's the "end of the world" for you.
On the other hand, the world of Revocs and Nudist Beach are very clearly an adult's world. It's about business and objectives, not petty games. The stage is the entire world, not just Japan. And people in this world have actually experienced death and consequence. Nui killed Ryuko's father, she didn't just "defeat" him. He cut her eye out, and she lost it for good. Tsumugu's also saw someone he loved killed in a Kamui experiment. The stakes in this world are totally different, and it's clear that Ragyo lets Satsuki continue with her little games because they're of little real consequence and it makes for good training to see if her daughter has what it takes to graduate into the adult world later.
So I really don't think there's a question as to what the outcome of a Satsuki vs Nui battle now would be. Nui exists and works in a world where Satsuki's ambitions are just a grain of sand.