A truly fitting punishment would be that Boeing is prohibited from piggybacking certification of any further 737 variants.
Slapping a 5th layer on top of the current crud for a new version is simply not realistic. Removing layers to allow for a new version is also not realistic, as the certification requirements would be pretty close to those of a clean-sheet aircraft.
So in conclusion, Boeing got away with certifying an aircraft that should never have been certified in the first place, and will reap the financial benefits of it. Minus some minor compensation to airlines and victims.