I don't have anything to cite this, but I am under the impression that the motor is only for display purposes. If you look at the first row, you can see the back is not as large as compared to the back row (bigger bump out behind the seats). Also, it has a pole underneath the seats for the electronics/ restraint system plus a guide wheel that will assumingly assist in the seat leveling once in the station.I was under the impression that the rotations are controlled by a motor in the chassis assembly connected via the seat hub connector based on footage of the demo cars being spun while the chassis remains locked into position - therefore all forces could be easily calculable as part of the design phase since the rotation is known in advance.
In the Coaster Studios video that interviewed one of the S&S reps, they spoke about how they have a simulation to be able to predict the carts movement despite any weight differences in rider or the situation of the single riders. This leads me to believe that it will freely spin and won't have any motors.