To now start a re-design of the air frame, or part of it (Thus to remove the need for MCAS) will surely mean a new type approval needed and 737NG crews will not be able to fly such a
reincarnation on the same licence. (which was not part of the MAX deal to airlines as we know)
Doesn’t matter, that ship has sailed; a long time ago. Boeing no longer has the luxury to bow to commercial forces that originally demanded a ‘same type’ certificate. This has been a long story that can be traced as far back to the development of the NG and the demands Southwest Airlines, for one, maybe even further and possibly with others? Was the 800/900 NG not considered longitudinally unstable hence the requirement for the huge tail surface/rudder? Someone already mentioned that the fuselage of the 737 was never intended to be the length that it eventually became.