Ballistically, I don't think there's anything wrong with the WSMs or WSSMs. Perhaps the problem is one of saturation: they simply do not offer enough improvement over existing rounds to warrant the cost of a new rig and accessories such as reloading dies. There are no gaps left to fill except between the .308 Win and the .30-06.
But, a 7mm-.50 Cal Browning MG could prove interesting.
