If it does fit on, then airbags would be a thing to check if they are suitable, as they are designed for each car. I doubt an insurance company would be too impressed with taking out the airbag to fit a S1 XM wheel
One thing I dislike about the C5s is the steering finish on the higher trim levels, its supposed to be leather, though its not, more like leather look. Over time it goes funny, it shuffles up and makes the steering wheel bobbly and sticky when in hot weather. I have seen high mileage cars with good wheels on and low mileages ones with awful finishes. Some people have said if touching the wheel with fuel on your hands of moisturiser then this runins the finish.
I have a spare wheel in the garage from a more basic C5 which doesnt have the leather effect, incase mine turns out like that. So far its perfect though.