Just to clarify something assuming FLCH on a Boeing is equivalent to OP DES on the Airbus: Airbus prohibits use of OP DES (on the A320 and I imagine across the board) if altitude in the FCU is set lower than 500' or MDA/H, whichever is highest.
Ok, that's good. Having flown both A and B aicraft I have never tested that, and I can't see any situation where I would use FLCH or open descend with selected altitude lower than FAF alt. And I didn't know there is such logic that you described in Airbus even though I believe I know the Airbus logic quite well.
Why don't they fix the bug in Boeing? Why don't they build planes that can't be flown to any unsafe conditions? Why is it possible to shut down all engines airborne? Why is it possible to switch off flight instruments and IRU's airborne? Why is it possible that both pilots open their seat belts at the same time if the plane is flown in severe turbulence?
Why do they build cars that can be driven straight to a stone wall?
It is not possible to build such automation that lets crew fly the plane in all possible cases, but prevents them to do anything that might lead the plane to danger. Understanding and controlling plane's energy level while flying an approach is still pilots' job, automation doesn't understand what lies ahead. There are many cases where the automation doesn't work as it should, and the automatic systems are very stupid if things don't go as they should. That's why the pilots are needed in the cockpit. And the pilots shouldn't be stupid or sleeping. This "FLCH trap" is not something that can ever happen in final approach if the pilot's have brain in their heads.