This is interesting and makes sense to me. Especially when you consider the time it takes to do it the "old" way. Time is money and technology has come a long way so I can see where doing a flush with the method you described would be a good route to go. My only question is regarding the countless posts where people are claiming transmission problems after doing a flush. Is this likely the small percentage with a bad experience being the loudest? And people who do the flush without issue just aren't vocal because there's no issue? I'm at 70k and have not had a transmission service, but I did have my valve bodies replaced under warranty at 50k so I'd like to think they did not put the old fluid back in, but I have a hard time trusting places to do things correctly.
I had the same thought as this. Seems like a much easier way to refill back to the correct level, if you wanted to drop the pan and change the filter.