Okay, so Boeing added an electronic safety feature (with a deadly failure mode) necessitated by physical changes and regulation. They didn't mention it for marketing reasons. They made an indicator of the deadly failure mode of the feature a paid option. Got it.
Reading a little between the lines this is probably related to the pitch - power coupling present on all modern airliners. This is due to the thrust line being below the centre of lift meaning that increasing power causes a pitch up moment.
In the 737 Max this probably got exacerbated to the point that it was possible to fly the plane into a stall by sharply increasing power in a high AoA situation (typically in a go-around). This was probably different enough to the 737NG that they felt it necessary to add the MCAS system to prevent having to do, what they considered, excessive differences training in that phase of flight.
Could well be; I read somewhere that it was related to the ever bigger engines (for more efficient (higher) bypass ratio), which presumably have a lower centre of thrust.
They lengthened the nose gear 20cm to fit the new engines with the same ground clearance. Must have dropped the thrust centre line nearly half of that.
Well the Seattle Times quoted an ex-Boeing employee thusly:
> A former Boeing executive, speaking on condition of anonymity because discussion of accident investigations is supposed to be closely held, said that Boeing engineers didn’t introduce the change to the flight-control system arbitrarily.
> He said it was done primarily because the much bigger engines on the MAX changed the aerodynamics of the jet and shifted the conditions under which a stall could happen. That required further stall protection be implemented to certify the jet as safe.
