Here are two important parts of the story that we do not know as yet so far as I am aware.
1.) What are the aerodynamic characteristics or aberrations that led to MCAS?
2.) How many times (if any) has the MCAS been activated besides the two Lion and one ET flights? Has MCAS ever been activated when there was no malfunction in the AoA?
Bend a Lot, while I am aware of grandfather rights, I have no idea how much content on the MAX would be verboten or obsolete if a separate type rating was required. Or invent a "sub-type rating". And I have no idea what the type rating has to do with the type certification of the aircraft! Just because an aircraft requires a type rating, why would that affect the type certification of the aircraft?