I started reading this thread because of the title, but I haven't seen anyone actually explain or show a demonstration of what they are defining as elbow power. I have been training in Hung Fa Yi Wing Chun alone with my Aikido training for the last 4years. HFY has this concept of elbow power/energy as a fundamental part of the art. They also use wrist energy and other things depending on range and situation. It is quite simple to understand and has transformed my Aikido. It's all about physics, body alignment and structure with proper intent. I can now see and feel for myself why techniques succeed or fail based on simple geometry. I've been to a number of seminars outside my area since learning this stuff and I find myself easily moving uke's around that I used to have trouble with.
I have no idea what Dan does, but I took a short class with Popkin Sensei recently. I found many of his principles to be identical or nearly so to the HFY concepts, and shared that with him then. He has good stuff, but I'm getting very similar concepts in my HFY training and have limited time so I can't really explore that right now with my schedule.
Elbow power as "a principle" or a technique is not what we do. It is imbedded in a type of movement we utilize, so that elbow power is not something you need to think about it....it happens. I could say the same thing with our knees.
As has been pointed out; various higher level arts have similar theories. I think the most strident failure is folks not understanding In yo ho (yin yang method) and intent, so they end up mimicing movement they see, without ever attaining the power and softness therein.
From what I have seen of Hung ga Yi your use of the body and arm as a frame would pretty much nullify what we are trying to accomplish. Of course there are other similar things as in all arts. I think it would be better to look at a combination of Koryu, Chen taiji and FMA to relate to what we do. Elbow is not independent from the body- to the wrist- to the hand. Everything works in a series of three from feet to finger.