I expect some of that is true.The fuel economy is very good on the MX admittedly.ISX has never been brilliant with fuel econom.EGR caused some head aches,I cant really see the need of it when Urea is now readily accepted.Where the MX will gain ground is in maintenance times,top end sets now only consist of valve clearances as against early ISX where injector preload has to be set to.The average workshop personal may find the valve train a bit daunting on ISX.I think the limiting factor will be MX reliability which even in the UK is not brilliant.