The simple solution would be to just remove MCAS and take the certification as a new plane. Boeing might have to eat the retraining costs but it's got to be better than eating the cost of the planes should they be deemed unfit for purpose and Boeing sued by every airline to recoup the costs of the now useless planes.

There's also the possible hardware fix to add an additional AoA sensor and change the software to limit the total deflection allowed + add a way to disable the MCAS only while keeping the electronic trim. The plane itself isn't irredeemable by a long shot though.