There should be more coasting with no gear engaged and low gear low rpm for low loads, than what automatics chose in practice.
But I don't have any data at hand for practical fuel efficiency and modern automatics versus manual.
The latest ones do, being integrated with GPS and a terrain database to anticipate changes.
for at least 20+ years now BMW/Porsche/VW also use the onboard IMUs and gyros and wheelspeed sensors to determine whether or not a shift should happen , say, in the middle of a long high speed banking turn.
Mercedes Glide Mode for example does this automatically to increase MPG (allegedly).
I think it is accurate enough to think of each revolution as a fixed cost for 'low' or idle power.
At idle power the motor should probably only be engaged when also braking.
a cars' stability is aided by engine braking; if that isn't there it must be accommodated by knowledge of such a fact by the ABS/TCS/VCS systems, or a skilled driver that is expecting it.
A regular car that expects engine braking, thrown into neutral and coasting down the highway is a more fragile handling and car-dynamics situation without these precautions. The Mercedes Glide Mode accommodates this by using the ABS/TCS systems to keep the weight where it needs to be regardless of applied engine torque one way or another; the driver does not experience a differently handling car.
Or is there some effect in the rubber from engine braking that make the front wheel more "prepared"?