It may be that the reason that this sort of training was not handed down to future Aikidoists was because Ueshiba himself did not encourage it in a practical way. I recall a story from somewhere that O'Sensei once came upon a group of his students who trying to make the techniques work martially and were struggling with one another. He became annoyed saying that he had spent a lifetime studying these things so they didn't have to start there. O'sensei was, evidently, interested in something else.
This train of thought is more or less the standard fair expressed through many teachers in Aikido. I find it wildly inconsistent with virtually every aikido demo and every shihan and teacher I have ever felt. It is they-who are in fact still struggling with trying to make things work. It could equally be said that Ushiba was trying to free their minds. Further, I would share from my own experience that of those who train with me (who come from many different arts) and continue to grow in internal skills-they all seem to arrive at the same conclusions.
1. As their power grows they increasingly become disinterested in fixed arts of any kind. In many ways they find them stiffling and stilted. IP/Aiki is without form and therefore without style or art.
2. When I speak to them about a "feeling" that will build in them, a feeling akin to living free in the world and changing them from within, they have scoffed, later almost to a person, they come back to tell me it is happening to them.
This leads me to my own personal interest in your last comments:
My own sense is that he was deeply exploring how this training could connect his essence to the greater universe from whence he was born and back to which he must die. It is possible that his interest in Internal Power dropped away in this pursuit along with a lot of things. In any case, most of his direct students couldn't understand what the dickens he was talking about when he lectured and he certainly didn't develop a clear method for his students to follow for increasing internal power.
I don't mean to dismiss anyone's interest in pursuing this direction. There is nothing in it that I can see that is contrary to Aikido practice - Indeed it can only enrich it. I just raise the possibility that internal training wasn't central to O'Sensei's spiritual quest and therefore only remains in today's Aikido in vestiges.
It is my belief that it was his pursuit of IP/aiki (something which he NEVER stopped talking about, which was in fact THEE cause of his transformation. It was not something he ever left behind, Don. rather it was something he was racing toward. I would contend that once he realized how powerful and free one could be at every moment he recognized how that could be a powerful transformative experience for many people.
Consider that many of the early Uchi deshi were rough and tumble guys, consider what the demeanor has always been for the majority of those who enter martial arts; in many cases it boils down to resolving issues with fear or dominance. It is clear Ueshiba had these same issues, so did Takeda. I believe Ueshiba's vision was in finding a way out, I also believe that today, we wouldn't even know his name, if it were not for the power (IP/aiki) that energized his vision and gave it physical credibility.
As I continue to get out and meet more of your teachers and Shihan face to face, as well as many other teachers from different arts it is becoming increasingly obvious to all in the room what it really means to have been "released" from form and what it looks like to operate freely and with impunity, and more's the point... to have the "actual" power to resolve conflict to a peaceful conclusion.
Why was his "vision" embroiled with conflict?
Trying to tie fighting and the mundane nature of hand-to-hand, together with IP/Aiki is fundamental flaw. Ueshiba's "vision" continued to be expressed through martial arts. That alone should speak loudly to all involved. He recognized an indelible truth, written into our deepest nature, and he knew the way out. It was his choice to express his spirituality through facing conflict and resolving it, not apart from it.
Why no one understood
I have long felt the dissonance that existed between he and his students was profound. Yet it is worth noting that it appears the one student who pursued the path of IP/aiki, Tohei, was recognized and given a "finished" diploma 10th dan.
Honestly, I do not think that anyone then, or now could have understood him or truly capture his vision without IP/Aiki. Freedom from conflict, comes through IP/Aiki. Everything else is just martial arts.