Mine has tried to downshift when I let off the gas at highway speeds twice, once before the update and once after, so I'm going to say it didn't work. At least it tries to works it way down through the gears and never has shifted straight to first.
From what Ford filed with the NHTSA this update appears to be only intended to prevent the dangerous downshift to first gear when the output speed sensor fails (intermittently or otherwise). The current firmware interprets that condition as the vehicle has slowed down and first gear is appropriate because the OSS reads "zero RPM." The firmware update changes the behavior so that if a few milliseconds ago we were going 50 MPH and now we are going 0 MPH something is obviously wrong so don't shift to first gear. The other part of the update will cause the MIL to display so that you'll get the OSS serviced. Previously there would be no indication to the driver, other than the abrupt change to first gear , that anything had malfunctioned. I don't think we'll notice any change in the normal behavior after the update (and indeed I only noticed sharper shifts during the "training" period as the dealer warned me about, but those smoothed out pretty quickly and I see absolutely no difference now in how the transmission behaves after the most recent update).
This is sadly similar to the engineering snafu plaguing Boeing right now with the 737 MAX. Failing to validate input data for valid ranges and transitions on a single-sensor control system isn't good engineering practice. This was a "bug" and Ford (hopefully) fixed it the second time.