The single most important difference for me in my VL PRR Centipede AA set is both units have full power, smoke, and SOUND. Legacy AA sets have only one engine with power and sound; the other is a dummy. (Also, if there was a B unit available with power it did not have sound.) This required that you buy two complete AA sets to get two powered and sound units. Buying two Legacy sets to get power/sound in both units drove the cost up to near VL prices. And you would not get the VL feature of the two engines being out of sync which is really neat.
Because the Centipedes had full power, smoke, and sound in each unit I assume all future VL AA, AB, and even ABA sets will too. If they issue them in PRR, I will buy.
PS: they do not need to be brass.