That sounds good in theory, but who is flying around an airliner at their ' aerodynamic ceiling' ?
Don't dismiss the matter too lightly because:
1. Not all aircraft are airliners and some ( U2, SR71 and some military) may well operate close to their absolute ceiling.
2. Even at the 1.3 g ceiling the usable speed range between the buffet boundaries is unlikely to extend from Vmd to 1.32Vmd.
It appears, therefore, that Vmd ceases to be an option above a certain height (for subsonic aircraft at least) because it would be below the stall speed, and Vmr may ultimately be unobtainable due to the limiting Mach Number and wave drag. I guess that in that case, for max range you need to fly just below Mcrit to avoid wave drag, and for endurance you just fly as slow as you can with a safe margin above the stall.
Aircraft routinely cruise at speeds (slightly) above Mcrit. The problem occurs when Mcdr (Critical drag rise mach number) is exceeded.
As altitude increases, compressibility causes the TAS value of Vs to increase while the TAS value of Mcdr decreases. This causes the buffet boundaries to converge towards a single speed at the absolute ceiling.