MCAS seems so deeply rooted in the 737 MAX's flight control systems it seems pretty obvious to most of us here that Boeing still cannot fathom out, nor procure a safe fixable software rewrite/redesign/patch solution, (whatever you want to name it) to gain back the aircraft's stability thus to get it back in line with it's 1967 737-100/200 type approval Grandfather rights certificate,
Thus the current 737 MAX air frame is unstable (as is) in certain flight envelopes, thus un-certifiable on that old type ticket approval.(and likely should never have been approved)
Which is we we are at right now with all new production halted after months of soothing noises, and lots of hand wringing, but NO fix.
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)