Fairly obviously, it will be very difficult for the FAA to certify a fix without first having a review of the FDR of the Ethiopian flight. Further difficulties are likely because other authorities may not approve certification without independent assessments of the "fixes". The only solution will be considerably more transparency from the FAA and the Boeing. Public opinion is the final arbiter for the future of the the MAX aircraft and perhaps even Boeing itself.
Having read the contributions, there is still considerable controversy about how the AOA/MCAS/Automation systems actually operates in ALL circumstances. While it seems the intention that MCAS is triggered in manual flight without flaps; it is not absolutely clear what are all the circumstances that it may maintain authority. Certainly, autopilot would appear to be disabled, and even if it were not, it may be affected by AOA errors. It is also not clear that a flap condition totally disables MCAS in all circumstances. There are also discrepancies over the left/right authority and the left and right seat controls and feedback. Above all it is fairly clear that the automated controls are inappropriately attempting to force a nose down condition that must be "rescued" by pilots. It is also not clear that there is enough time available to pilots to rescue that erroneous condition.