I am glad to learn that massive objects don't disappear into empty space. But I think we should probably prepare ourselves. Art Bell may have a guest soon that tells us that is exactly what will happen when that asteroid hiding behind the moon crashes into earth next month.
It isn't necessary to postulate disappearing mass to see that a reference frame traveling in the space-time continuum of general relativity, represented by smooth curved space, will undergo varying rates of acceleration. But every object in that reference frame undergoes the same varying rate. If the car is in outer space, the cup of coffee on the dash board doesn't slide.
Not all accelerations are due to gravity modeled as smooth curved space. For the car traveling down a road on earth, the acceleration is due to the friction force between the tires and the road. The frame of the car undergoes acceleration, but not the coffee. So the coffee slides. The same would be true of a car in outer space being tossed around by thrusters firing erratically on the outside of the car. The frame of the care would accelerate, but not free objects in the car until they bump into something.
We are talking about two different scenarios. There is no need to invent mysteriously created fictional forces for the car on earth.
The point being, the General Relativity allows for such interpretation, not whether there is any need to do so.
I agree that complex scenarios emerge when acceleration is not constant. Likewise when loose objects are acted upon by a changing gravity field. Do we need to discuss them, to further condemn Luther?
There might be weak vs. strong equivalence principles in play, but to do so I need to refresh my knowledge of physics, which is nearly as old as Carl Sagan.