Except that, when the C-(or D-) scalers become the majority, there's no saving anymore for the company in raising their benefits while reducing the benefits of the minority who's going to disappear (retire) eventually.
Unless of course if they had to improve the C-scale conditions anyway in order to make them stay. Then saving a little money on the side by hitting the expensive minority would certainly be something they will try.
But in summary, if you believe the company would be interested in a middle ground between B- and C-scale, keep dreaming, that would just cost more than it does today.