CAS is determined by taking the compressibility of air into consideration. Until the physical properties of air change there's absolutely no reason to discard the present calibration law. EAS on the other hand is not a physically meaningful quantity. EAS tells you absolutely nothing about compressibility. It is a fictitious speed resulting from the setting of rho to its ISA MSL value in the dynamic pressure equation.
Let's get it right shall we.
The equations used to calibrate airspeed indicators are intended to account for compressibility when calculating
EAS from measured total and static pressures. This involves a Mach Number correction. The relationship between EAS and Mach Number varies with pressure altitude. To permit a standard calibration all airspeed indicators are calibrated using the EAS/Mach relationship that exists at sea level. At any other altitude the airspeed (CAS) indicated by the instrument is not a true indication of the speed that governs aircraft forces (EAS). To calculate forces on the aircraft the meaningful quantity for me is EAS not CAS, and it has served me well for over half a century now.
The speed read by a perfect airspeed system (zero instrument and static error) with the Mach Number correction based on a standard day sea level relationship between EAS and Mach Number is the calibrated airspeed. At sea level the correction is exact, but not at any other altitude.
Note the emphasis - CAS is intended to give a correct value of EAS, which is the only relevant quantity for any calculation of aerodynamic forces. As noted, CAS tells you nothing about dynamic pressure which is the standard non-dimensionalising pressure when calculating and using aerodynamic coefficients.
Logically I'm with Rivet-gun in that we now have the computing ability to present the more meaningful EAS, but I shudder to think of the confusions and possible risks associated with any change!