The FAA use of the words "too expensive" typically refer to mandated requirements that go beyond current regulations governing all aircraft in class.
Thus it is presumed that the current regulations are safe enough if all procedures and design requirements are followed. To go beyond this requirement places an additional burden on the economics of design and manufacture or operating an aircraft and as such a demonstration of benefit must be shown versus retro of a fleet.
There are two critical items mising in the plethora of words on internet boards.
The facts are not yet obvious to us: were presumed procedures followed or if not should that not be where corrective action is easier taken?
What are all costs associated with mandated changes over and above current requirements, taken into account , out of service time, hangar costs, manpower available, cost of parts, etc. versus number of lives saved, versus number of lives lost becuase the proposed change is never perfect and may result in causing a different type of accident?
So we can continue our "what if" discussions but lets be careful about presuming how simple a fix is for somebody else to adopt.