Here is my opinion... and it's just that... for what 2 cents it is worth...
There is nothing wrong with diving Back Plates and Wings in and of itself. The problem lies in that not many people are using them. Now there may be areas of the country and within specific little groups of divers (that have been sold on their benefits) that this is not true... however I've been diving a lot - in fact, I dive almost every day... and no matter where I go on earth, there might be 1 or 2 BP/W set ups for every 20 divers.
Usually these are set up by advanced divers, often aspiring tech divers with specific configurations etc... The average recreational diver is not using them... and the average person taking the Rescue course is not using them. My entire point here is that using them to take classes amongst a group of people that will never use them and likely never even see someone with one on, is ridiculous. People should train with people of like minds. If everyone you're ever going to dive with is wearing a regular old jacket style or back inflate BC... then do your rescue practices in that gear. If everyone is wearing BP/W then by all means use them in the class. Mixing the two is confusing and accomplishes nothing.
For those that might argue that it is good for each to know and understand what the other is wearing, there is some validity to that... however most likely, things that aren't seen, worked with and practiced regularly will likely be lost on most... and the benefit of having learned with it is lost as well.
I'm an Instructor, Dive Guide, Dive Business Owner and have been diving all over the world... I would honestly say that outside of tech divers, less than 1 in 100 divers is diving BP/W... and while that number is slightly increasing... it is simply because LDS's are brainwashing people into spending more money for something that is less efficient and more costly to the diver.
Again, these are my opinions, but they are backed by experience... so Happy Diving to All.