Just to address a misconception
alone, unpowered, the craft is not 'aerodynamically stable'.
I don't believe this is true.
The problem addressed by MCAS is not specifically unpowered flight but flight when the aircraft has a high angle of attack. Because of the need to mount the wider engines further forward to maintain ground clearance, there is a tendency for the engine housing to cause additional aerodynamic forces that rotate the aircraft in the pitch axis - these forces tend to push the nose up. The forces are higher than on prior 737s.
By "unpowered" you might be thinking more of electrical power than engine power. The two are usually related. However any aircraft like the 737 has multiple electric power generators, if the generators on both main engines fail, there is a Auxiliary Power Unit (APU) that can provide electrical power. If both engines and the APU fail, many aircraft have a ram air turbine (RAT) that deploys to produce hydraulic and/or electric power. If both engines, the APU and the RAT fail, there are batteries that provide enough power for minimal necessary controls for a short while, maybe of the order of 30 mins.
I don't know about the 737, but the 30-year-old A320 family of fly-by-wire aircraft has a mechanical backup mode where the pilot can control the aircraft using purely mechanical means and non-electrical instruments. In 30 years I think the closest any aircraft has come to this was a 2005 A319 incident where the cockpit went dark and I believe the pilot flew for a while without any computerised aids, they quickly restored power and continued to their destination. I know of no reason to think the 737 is more dependent on computers for stable flight.
Even without any electrical power, an aircraft like the 737 ought to be no less "aerodynamically stable" than the earliest 737.
It is normal for aircraft trim to be adjusted during various phases of a flight. The aircraft is still considered 'aerodynamically stable'. When commencing an unpowered glide, the pilots would likely adjust trim. This applies to almost all aircraft.
It is normal that an aircraft in flight, without manual control inputs and without automated inputs from an autopilot etc, can exhibit undesirable flight characteristics such as a phugoid cycle. An aircraft with this sort of behaviour is normally regarded as aerodynamically stable.
I have not read anything to suggest the 737 NG or MAX series are inherently unstable. Even in an unpowered glide.
So far as I know, the only aircraft that are deliberately made inherently unstable are high-agility fighter aircraft.
MCAS stands for Maneuvering Charactersitics Augmentation System. From what I've read, a large part of the motivation for it was to make the aircraft controls feel the same as an older generation 737 - hence the name. Boeing felt that a pilot getting out of an older 737 could get into a 737-MAX and use & experience the same forces on the control yoke as before when climbing out after take off etc.