If you all recall, this is exactly what AA was trying to do when it introduced the Executive Platinum Level. It was originally a points based system where you would receive higher points per mile depending on your fare basis: First, Business, Full Y, and Discounted Y. I was a long time AA flyer before switching over to UA before they introduced the Executive Platinum Level. I didn't come back originally because most of my travels are in discounted Y and some C class, thereby making the level harder to obtain then say UA 1K.
Upon conception, the AA Exec Platinum was a great program to reward higher revenue flyers. The point-based system only lasted one year I believe, since now Exec Platinum can be attained on miles--100K. I am not sure if the point-based system is still in place.
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SA