I'm fascinated because it is the first time anybody associated with aikido has mentioned it where I could read/hear it.
Many years ago my myofascial therapy guy (who appears to have vanished into the Yucatan peninsula sometime before/during their last big hurricane) taught me how to isolate and use the muscles that pull the shoulder blades down and together from below, as a posture correcting maneuver.
I do find myself doing it on the mat as part of my preparation for training; now I'll have to think about why and what role it seems to be playing.
Do you have more information about it?
The first person I heard talk about it was Akuzawa Sensei when he was at our dojo. The context was slightly different... He was showing some conditioning exercises and they involved pulling the shoulder blades together. Most of his description centered around developing power by bring everything to the spine.
I was playing with a static technique shortly after his seminar and noticed that when I slid my shoulder blades together (without tightening the shoulder muscles) the partner fel slightly into my space. I started messing with it and realized that this was how you brought the power you received from the partner to your spine. It is in everything!
Ushiro Kenji was teaching at the Rocky Mountain Summer Camp the last three years and I asked him about it and his response was more less "of course"... Their guys learn it from their kata. It's part of the myriad structural details which are hidden in quite ordinary kata.
Ushiro Sensei actually had a bunch of drawings he used for class. At first I didn't quite get them... they were ovals with little dots and arrows pointing from one to another. I finally realized that the ovals were a top down view of a body and the dot was the spine. The arrows were the power of the attack and the whole thing was about how to take the power of the attack, in this case coming from two points of contact on the shoulders into a single point i.e. the spine.
This is HUGE! It is in everything, or should be. When you combine the shoulder blade element with an understanding of what happens when you tuck your tail bone, your Aikido goes to an entirely different level. The tail bone straightens the spine and allows the pelvis to rotate forward. When this happens, the energy in your arms starts aiming upwards so that when the partner grabs you he is automatically being taken up off his base. This all comes from the core without the arms tensing at all.
Normally, when folks get grabbed at two points of contact, they try to rotate the hips to turn but that merely ends up with one point pulling and the other point pushing, both are hitting the partner's structure. When you bring the shoulder blades togther, the power of the two contact points is brought to the single point of the vertical axis of the spine. At that point truning is effortless.
I think this whole thing is absolutely emblematic of the mess that is the Aikido teaching methodology, or lack thereof. These are relatively simple mechanical things that other arts are quite aware of and consider to be foundational. Yet most of us in Aikido trained for years without ever hearing a mention of these things from our teachers. No wonder we couldn't duplicate what our teachers were doing...