Boeing created a fundamentally less stable plane (
source) in order to realize a few percent efficiency improvement. To compensate for the
inherent flaw, they implemented a new
automated correction system with a
single point of failure and
not documented in pilot manuals or trainings.
There are several similarities between the Lion flight and the Ethiopian flight. Both had erratic speed and climb/elevation readings, both the pilots requested to return to origin, and both crashed in a steep drop within 5-15 minutes of takeoff.
The automated system mentioned above seems by all accounts to be the primary cause of the Lion pilots' struggle with the aircraft. After the crash the system became widely known, and while I hope all pilots of that model received training on disabling the automated system, but from what I can find Boeing has not issued any change to the behaviour of the system, simpler override procedure, or a secondary point of failure.
Boeing is being sued in US courts by the families of Lion passengers, but I think Boeing was very "lucky" that Lion JT610 was operated by an airline with an already dubious safety record and the passengers were all Indonesian and just one Italian. In the case of the Ethiopian flight, I have seen reports that 35 nationalities were on-board, including many Americans and Europeans, so this crash is likely to receive a much higher level of attention and scrutiny in international media.